Source file src/cmd/compile/internal/ssa/check.go

     1  // Copyright 2015 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package ssa
     6  
     7  import (
     8  	"cmd/compile/internal/ir"
     9  	"cmd/internal/obj/s390x"
    10  	"math"
    11  	"math/bits"
    12  )
    13  
    14  // checkFunc checks invariants of f.
    15  func checkFunc(f *Func) {
    16  	blockMark := make([]bool, f.NumBlocks())
    17  	valueMark := make([]bool, f.NumValues())
    18  
    19  	for _, b := range f.Blocks {
    20  		if blockMark[b.ID] {
    21  			f.Fatalf("block %s appears twice in %s!", b, f.Name)
    22  		}
    23  		blockMark[b.ID] = true
    24  		if b.Func != f {
    25  			f.Fatalf("%s.Func=%s, want %s", b, b.Func.Name, f.Name)
    26  		}
    27  
    28  		for i, e := range b.Preds {
    29  			if se := e.b.Succs[e.i]; se.b != b || se.i != i {
    30  				f.Fatalf("block pred/succ not crosslinked correctly %d:%s %d:%s", i, b, se.i, se.b)
    31  			}
    32  		}
    33  		for i, e := range b.Succs {
    34  			if pe := e.b.Preds[e.i]; pe.b != b || pe.i != i {
    35  				f.Fatalf("block succ/pred not crosslinked correctly %d:%s %d:%s", i, b, pe.i, pe.b)
    36  			}
    37  		}
    38  
    39  		switch b.Kind {
    40  		case BlockExit:
    41  			if len(b.Succs) != 0 {
    42  				f.Fatalf("exit block %s has successors", b)
    43  			}
    44  			if b.NumControls() != 1 {
    45  				f.Fatalf("exit block %s has no control value", b)
    46  			}
    47  			if !b.Controls[0].Type.IsMemory() {
    48  				f.Fatalf("exit block %s has non-memory control value %s", b, b.Controls[0].LongString())
    49  			}
    50  		case BlockRet:
    51  			if len(b.Succs) != 0 {
    52  				f.Fatalf("ret block %s has successors", b)
    53  			}
    54  			if b.NumControls() != 1 {
    55  				f.Fatalf("ret block %s has nil control", b)
    56  			}
    57  			if !b.Controls[0].Type.IsMemory() {
    58  				f.Fatalf("ret block %s has non-memory control value %s", b, b.Controls[0].LongString())
    59  			}
    60  		case BlockRetJmp:
    61  			if len(b.Succs) != 0 {
    62  				f.Fatalf("retjmp block %s len(Succs)==%d, want 0", b, len(b.Succs))
    63  			}
    64  			if b.NumControls() != 1 {
    65  				f.Fatalf("retjmp block %s has nil control", b)
    66  			}
    67  			if !b.Controls[0].Type.IsMemory() {
    68  				f.Fatalf("retjmp block %s has non-memory control value %s", b, b.Controls[0].LongString())
    69  			}
    70  		case BlockPlain:
    71  			if len(b.Succs) != 1 {
    72  				f.Fatalf("plain block %s len(Succs)==%d, want 1", b, len(b.Succs))
    73  			}
    74  			if b.NumControls() != 0 {
    75  				f.Fatalf("plain block %s has non-nil control %s", b, b.Controls[0].LongString())
    76  			}
    77  		case BlockIf:
    78  			if len(b.Succs) != 2 {
    79  				f.Fatalf("if block %s len(Succs)==%d, want 2", b, len(b.Succs))
    80  			}
    81  			if b.NumControls() != 1 {
    82  				f.Fatalf("if block %s has no control value", b)
    83  			}
    84  			if !b.Controls[0].Type.IsBoolean() {
    85  				f.Fatalf("if block %s has non-bool control value %s", b, b.Controls[0].LongString())
    86  			}
    87  		case BlockDefer:
    88  			if len(b.Succs) != 2 {
    89  				f.Fatalf("defer block %s len(Succs)==%d, want 2", b, len(b.Succs))
    90  			}
    91  			if b.NumControls() != 1 {
    92  				f.Fatalf("defer block %s has no control value", b)
    93  			}
    94  			if !b.Controls[0].Type.IsMemory() {
    95  				f.Fatalf("defer block %s has non-memory control value %s", b, b.Controls[0].LongString())
    96  			}
    97  		case BlockFirst:
    98  			if len(b.Succs) != 2 {
    99  				f.Fatalf("plain/dead block %s len(Succs)==%d, want 2", b, len(b.Succs))
   100  			}
   101  			if b.NumControls() != 0 {
   102  				f.Fatalf("plain/dead block %s has a control value", b)
   103  			}
   104  		case BlockJumpTable:
   105  			if b.NumControls() != 1 {
   106  				f.Fatalf("jumpTable block %s has no control value", b)
   107  			}
   108  		}
   109  		if len(b.Succs) != 2 && b.Likely != BranchUnknown {
   110  			f.Fatalf("likeliness prediction %d for block %s with %d successors", b.Likely, b, len(b.Succs))
   111  		}
   112  
   113  		for _, v := range b.Values {
   114  			// Check to make sure argument count makes sense (argLen of -1 indicates
   115  			// variable length args)
   116  			nArgs := opcodeTable[v.Op].argLen
   117  			if nArgs != -1 && int32(len(v.Args)) != nArgs {
   118  				f.Fatalf("value %s has %d args, expected %d", v.LongString(),
   119  					len(v.Args), nArgs)
   120  			}
   121  
   122  			// Check to make sure aux values make sense.
   123  			canHaveAux := false
   124  			canHaveAuxInt := false
   125  			// TODO: enforce types of Aux in this switch (like auxString does below)
   126  			switch opcodeTable[v.Op].auxType {
   127  			case auxNone:
   128  			case auxBool:
   129  				if v.AuxInt < 0 || v.AuxInt > 1 {
   130  					f.Fatalf("bad bool AuxInt value for %v", v)
   131  				}
   132  				canHaveAuxInt = true
   133  			case auxInt8:
   134  				if v.AuxInt != int64(int8(v.AuxInt)) {
   135  					f.Fatalf("bad int8 AuxInt value for %v", v)
   136  				}
   137  				canHaveAuxInt = true
   138  			case auxInt16:
   139  				if v.AuxInt != int64(int16(v.AuxInt)) {
   140  					f.Fatalf("bad int16 AuxInt value for %v", v)
   141  				}
   142  				canHaveAuxInt = true
   143  			case auxInt32:
   144  				if v.AuxInt != int64(int32(v.AuxInt)) {
   145  					f.Fatalf("bad int32 AuxInt value for %v", v)
   146  				}
   147  				canHaveAuxInt = true
   148  			case auxInt64, auxARM64BitField, auxARM64ConditionalParams:
   149  				canHaveAuxInt = true
   150  			case auxInt128:
   151  				// AuxInt must be zero, so leave canHaveAuxInt set to false.
   152  			case auxUInt8:
   153  				// Cast to int8 due to requirement of AuxInt, check its comment for details.
   154  				if v.AuxInt != int64(int8(v.AuxInt)) {
   155  					f.Fatalf("bad uint8 AuxInt value for %v, saw %d but need %d", v, v.AuxInt, int64(int8(v.AuxInt)))
   156  				}
   157  				canHaveAuxInt = true
   158  			case auxFloat32:
   159  				canHaveAuxInt = true
   160  				if math.IsNaN(v.AuxFloat()) {
   161  					f.Fatalf("value %v has an AuxInt that encodes a NaN", v)
   162  				}
   163  				if !isExactFloat32(v.AuxFloat()) {
   164  					f.Fatalf("value %v has an AuxInt value that is not an exact float32", v)
   165  				}
   166  			case auxFloat64:
   167  				canHaveAuxInt = true
   168  				if math.IsNaN(v.AuxFloat()) {
   169  					f.Fatalf("value %v has an AuxInt that encodes a NaN", v)
   170  				}
   171  			case auxString:
   172  				if _, ok := v.Aux.(stringAux); !ok {
   173  					f.Fatalf("value %v has Aux type %T, want string", v, v.Aux)
   174  				}
   175  				canHaveAux = true
   176  			case auxCallOff:
   177  				canHaveAuxInt = true
   178  				fallthrough
   179  			case auxCall:
   180  				if ac, ok := v.Aux.(*AuxCall); ok {
   181  					if v.Op == OpStaticCall && ac.Fn == nil {
   182  						f.Fatalf("value %v has *AuxCall with nil Fn", v)
   183  					}
   184  				} else {
   185  					f.Fatalf("value %v has Aux type %T, want *AuxCall", v, v.Aux)
   186  				}
   187  				canHaveAux = true
   188  			case auxNameOffsetInt8:
   189  				if _, ok := v.Aux.(*AuxNameOffset); !ok {
   190  					f.Fatalf("value %v has Aux type %T, want *AuxNameOffset", v, v.Aux)
   191  				}
   192  				canHaveAux = true
   193  				canHaveAuxInt = true
   194  			case auxSym, auxTyp:
   195  				canHaveAux = true
   196  			case auxSymOff, auxSymValAndOff, auxTypSize:
   197  				canHaveAuxInt = true
   198  				canHaveAux = true
   199  			case auxCCop:
   200  				if opcodeTable[Op(v.AuxInt)].name == "OpInvalid" {
   201  					f.Fatalf("value %v has an AuxInt value that is a valid opcode", v)
   202  				}
   203  				canHaveAuxInt = true
   204  			case auxS390XCCMask:
   205  				if _, ok := v.Aux.(s390x.CCMask); !ok {
   206  					f.Fatalf("bad type %T for S390XCCMask in %v", v.Aux, v)
   207  				}
   208  				canHaveAux = true
   209  			case auxS390XRotateParams:
   210  				if _, ok := v.Aux.(s390x.RotateParams); !ok {
   211  					f.Fatalf("bad type %T for S390XRotateParams in %v", v.Aux, v)
   212  				}
   213  				canHaveAux = true
   214  			case auxFlagConstant:
   215  				if v.AuxInt < 0 || v.AuxInt > 15 {
   216  					f.Fatalf("bad FlagConstant AuxInt value for %v", v)
   217  				}
   218  				canHaveAuxInt = true
   219  			case auxPanicBoundsC, auxPanicBoundsCC:
   220  				canHaveAux = true
   221  				canHaveAuxInt = true
   222  			default:
   223  				f.Fatalf("unknown aux type for %s", v.Op)
   224  			}
   225  			if !canHaveAux && v.Aux != nil {
   226  				f.Fatalf("value %s has an Aux value %v but shouldn't", v.LongString(), v.Aux)
   227  			}
   228  			if !canHaveAuxInt && v.AuxInt != 0 {
   229  				f.Fatalf("value %s has an AuxInt value %d but shouldn't", v.LongString(), v.AuxInt)
   230  			}
   231  
   232  			for i, arg := range v.Args {
   233  				if arg == nil {
   234  					f.Fatalf("value %s has nil arg", v.LongString())
   235  				}
   236  				if v.Op != OpPhi {
   237  					// For non-Phi ops, memory args must be last, if present
   238  					if arg.Type.IsMemory() && i != len(v.Args)-1 {
   239  						f.Fatalf("value %s has non-final memory arg (%d < %d)", v.LongString(), i, len(v.Args)-1)
   240  					}
   241  				}
   242  			}
   243  
   244  			if valueMark[v.ID] {
   245  				f.Fatalf("value %s appears twice!", v.LongString())
   246  			}
   247  			valueMark[v.ID] = true
   248  
   249  			if v.Block != b {
   250  				f.Fatalf("%s.block != %s", v, b)
   251  			}
   252  			if v.Op == OpPhi && len(v.Args) != len(b.Preds) {
   253  				f.Fatalf("phi length %s does not match pred length %d for block %s", v.LongString(), len(b.Preds), b)
   254  			}
   255  
   256  			if v.Op == OpAddr {
   257  				if len(v.Args) == 0 {
   258  					f.Fatalf("no args for OpAddr %s", v.LongString())
   259  				}
   260  				if v.Args[0].Op != OpSB {
   261  					f.Fatalf("bad arg to OpAddr %v", v)
   262  				}
   263  			}
   264  
   265  			if v.Op == OpLocalAddr {
   266  				if len(v.Args) != 2 {
   267  					f.Fatalf("wrong # of args for OpLocalAddr %s", v.LongString())
   268  				}
   269  				if v.Args[0].Op != OpSP {
   270  					f.Fatalf("bad arg 0 to OpLocalAddr %v", v)
   271  				}
   272  				if !v.Args[1].Type.IsMemory() {
   273  					f.Fatalf("bad arg 1 to OpLocalAddr %v", v)
   274  				}
   275  			}
   276  
   277  			if (v.Op == OpStructMake || v.Op == OpArrayMake1) && v.Type.Size() == 0 {
   278  				f.Fatalf("zero-sized Make; use Empty instead %v", v)
   279  			}
   280  
   281  			if f.RegAlloc != nil && f.Config.SoftFloat && v.Type.IsFloat() {
   282  				f.Fatalf("unexpected floating-point type %v", v.LongString())
   283  			}
   284  
   285  			// Check types.
   286  			// TODO: more type checks?
   287  			switch c := f.Config; v.Op {
   288  			case OpSP, OpSB:
   289  				if v.Type != c.Types.Uintptr {
   290  					f.Fatalf("bad %s type: want uintptr, have %s",
   291  						v.Op, v.Type.String())
   292  				}
   293  			case OpStringLen:
   294  				if v.Type != c.Types.Int {
   295  					f.Fatalf("bad %s type: want int, have %s",
   296  						v.Op, v.Type.String())
   297  				}
   298  			case OpLoad:
   299  				if !v.Args[1].Type.IsMemory() {
   300  					f.Fatalf("bad arg 1 type to %s: want mem, have %s",
   301  						v.Op, v.Args[1].Type.String())
   302  				}
   303  			case OpStore:
   304  				if !v.Type.IsMemory() {
   305  					f.Fatalf("bad %s type: want mem, have %s",
   306  						v.Op, v.Type.String())
   307  				}
   308  				if !v.Args[2].Type.IsMemory() {
   309  					f.Fatalf("bad arg 2 type to %s: want mem, have %s",
   310  						v.Op, v.Args[2].Type.String())
   311  				}
   312  			case OpCondSelect:
   313  				if !v.Args[2].Type.IsBoolean() {
   314  					f.Fatalf("bad arg 2 type to %s: want boolean, have %s",
   315  						v.Op, v.Args[2].Type.String())
   316  				}
   317  			case OpAddPtr:
   318  				if !v.Args[0].Type.IsPtrShaped() && v.Args[0].Type != c.Types.Uintptr {
   319  					f.Fatalf("bad arg 0 type to %s: want ptr, have %s", v.Op, v.Args[0].LongString())
   320  				}
   321  				if !v.Args[1].Type.IsInteger() {
   322  					f.Fatalf("bad arg 1 type to %s: want integer, have %s", v.Op, v.Args[1].LongString())
   323  				}
   324  			case OpVarDef:
   325  				n := v.Aux.(*ir.Name)
   326  				if !n.Type().HasPointers() && !IsMergeCandidate(n) {
   327  					f.Fatalf("vardef must be merge candidate or have pointer type %s", v.Aux.(*ir.Name).Type().String())
   328  				}
   329  			case OpNilCheck:
   330  				// nil checks have pointer type before scheduling, and
   331  				// void type after scheduling.
   332  				if f.scheduled {
   333  					if v.Uses != 0 {
   334  						f.Fatalf("nilcheck must have 0 uses %s", v.Uses)
   335  					}
   336  					if !v.Type.IsVoid() {
   337  						f.Fatalf("nilcheck must have void type %s", v.Type.String())
   338  					}
   339  				} else {
   340  					if !v.Type.IsPtrShaped() && !v.Type.IsUintptr() {
   341  						f.Fatalf("nilcheck must have pointer type %s", v.Type.String())
   342  					}
   343  				}
   344  				if !v.Args[0].Type.IsPtrShaped() && !v.Args[0].Type.IsUintptr() {
   345  					f.Fatalf("nilcheck must have argument of pointer type %s", v.Args[0].Type.String())
   346  				}
   347  				if !v.Args[1].Type.IsMemory() {
   348  					f.Fatalf("bad arg 1 type to %s: want mem, have %s",
   349  						v.Op, v.Args[1].Type.String())
   350  				}
   351  			}
   352  
   353  			// TODO: check for cycles in values
   354  		}
   355  	}
   356  
   357  	// Check to make sure all Blocks referenced are in the function.
   358  	if !blockMark[f.Entry.ID] {
   359  		f.Fatalf("entry block %v is missing", f.Entry)
   360  	}
   361  	for _, b := range f.Blocks {
   362  		for _, c := range b.Preds {
   363  			if !blockMark[c.b.ID] {
   364  				f.Fatalf("predecessor block %v for %v is missing", c, b)
   365  			}
   366  		}
   367  		for _, c := range b.Succs {
   368  			if !blockMark[c.b.ID] {
   369  				f.Fatalf("successor block %v for %v is missing", c, b)
   370  			}
   371  		}
   372  	}
   373  
   374  	if len(f.Entry.Preds) > 0 {
   375  		f.Fatalf("entry block %s of %s has predecessor(s) %v", f.Entry, f.Name, f.Entry.Preds)
   376  	}
   377  
   378  	// Check to make sure all Values referenced are in the function.
   379  	for _, b := range f.Blocks {
   380  		for _, v := range b.Values {
   381  			for i, a := range v.Args {
   382  				if !valueMark[a.ID] {
   383  					f.Fatalf("%v, arg %d of %s, is missing", a, i, v.LongString())
   384  				}
   385  			}
   386  		}
   387  		for _, c := range b.ControlValues() {
   388  			if !valueMark[c.ID] {
   389  				f.Fatalf("control value for %s is missing: %v", b, c)
   390  			}
   391  		}
   392  	}
   393  	for b := f.freeBlocks; b != nil; b = b.succstorage[0].b {
   394  		if blockMark[b.ID] {
   395  			f.Fatalf("used block b%d in free list", b.ID)
   396  		}
   397  	}
   398  	for v := f.freeValues; v != nil; v = v.argstorage[0] {
   399  		if valueMark[v.ID] {
   400  			f.Fatalf("used value v%d in free list", v.ID)
   401  		}
   402  	}
   403  
   404  	// Check to make sure all args dominate uses.
   405  	if f.RegAlloc == nil {
   406  		// Note: regalloc introduces non-dominating args.
   407  		// See TODO in regalloc.go.
   408  		sdom := f.Sdom()
   409  		for _, b := range f.Blocks {
   410  			for _, v := range b.Values {
   411  				for i, arg := range v.Args {
   412  					x := arg.Block
   413  					y := b
   414  					if v.Op == OpPhi {
   415  						y = b.Preds[i].b
   416  					}
   417  					if !domCheck(f, sdom, x, y) {
   418  						f.Fatalf("arg %d of value %s does not dominate, arg=%s", i, v.LongString(), arg.LongString())
   419  					}
   420  				}
   421  			}
   422  			for _, c := range b.ControlValues() {
   423  				if !domCheck(f, sdom, c.Block, b) {
   424  					f.Fatalf("control value %s for %s doesn't dominate", c, b)
   425  				}
   426  			}
   427  		}
   428  	}
   429  
   430  	// Check loop construction
   431  	if f.RegAlloc == nil && f.pass != nil { // non-nil pass allows better-targeted debug printing
   432  		ln := f.loopnest()
   433  		if !ln.hasIrreducible {
   434  			po := f.postorder() // use po to avoid unreachable blocks.
   435  			for _, b := range po {
   436  				for _, s := range b.Succs {
   437  					bb := s.Block()
   438  					if ln.b2l[b.ID] == nil && ln.b2l[bb.ID] != nil && bb != ln.b2l[bb.ID].header {
   439  						f.Fatalf("block %s not in loop branches to non-header block %s in loop", b.String(), bb.String())
   440  					}
   441  					if ln.b2l[b.ID] != nil && ln.b2l[bb.ID] != nil && bb != ln.b2l[bb.ID].header && !ln.b2l[b.ID].isWithinOrEq(ln.b2l[bb.ID]) {
   442  						f.Fatalf("block %s in loop branches to non-header block %s in non-containing loop", b.String(), bb.String())
   443  					}
   444  				}
   445  			}
   446  		}
   447  	}
   448  
   449  	// Check use counts
   450  	uses := make([]int32, f.NumValues())
   451  	for _, b := range f.Blocks {
   452  		for _, v := range b.Values {
   453  			for _, a := range v.Args {
   454  				uses[a.ID]++
   455  			}
   456  		}
   457  		for _, c := range b.ControlValues() {
   458  			uses[c.ID]++
   459  		}
   460  	}
   461  	for _, b := range f.Blocks {
   462  		for _, v := range b.Values {
   463  			if v.Uses != uses[v.ID] {
   464  				f.Fatalf("%s has %d uses, but has Uses=%d", v, uses[v.ID], v.Uses)
   465  			}
   466  		}
   467  	}
   468  
   469  	memCheck(f)
   470  }
   471  
   472  func memCheck(f *Func) {
   473  	// Check that if a tuple has a memory type, it is second.
   474  	for _, b := range f.Blocks {
   475  		for _, v := range b.Values {
   476  			if v.Type.IsTuple() && v.Type.FieldType(0).IsMemory() {
   477  				f.Fatalf("memory is first in a tuple: %s\n", v.LongString())
   478  			}
   479  		}
   480  	}
   481  
   482  	// Single live memory checks.
   483  	// These checks only work if there are no memory copies.
   484  	// (Memory copies introduce ambiguity about which mem value is really live.
   485  	// probably fixable, but it's easier to avoid the problem.)
   486  	// For the same reason, disable this check if some memory ops are unused.
   487  	for _, b := range f.Blocks {
   488  		for _, v := range b.Values {
   489  			if (v.Op == OpCopy || v.Uses == 0) && v.Type.IsMemory() {
   490  				return
   491  			}
   492  		}
   493  		if b != f.Entry && len(b.Preds) == 0 {
   494  			return
   495  		}
   496  	}
   497  
   498  	// Compute live memory at the end of each block.
   499  	lastmem := make([]*Value, f.NumBlocks())
   500  	ss := newSparseSet(f.NumValues())
   501  	for _, b := range f.Blocks {
   502  		// Mark overwritten memory values. Those are args of other
   503  		// ops that generate memory values.
   504  		ss.clear()
   505  		for _, v := range b.Values {
   506  			if v.Op == OpPhi || !v.Type.IsMemory() {
   507  				continue
   508  			}
   509  			if m := v.MemoryArg(); m != nil {
   510  				ss.add(m.ID)
   511  			}
   512  		}
   513  		// There should be at most one remaining unoverwritten memory value.
   514  		for _, v := range b.Values {
   515  			if !v.Type.IsMemory() {
   516  				continue
   517  			}
   518  			if ss.contains(v.ID) {
   519  				continue
   520  			}
   521  			if lastmem[b.ID] != nil {
   522  				f.Fatalf("two live memory values in %s: %s and %s", b, lastmem[b.ID], v)
   523  			}
   524  			lastmem[b.ID] = v
   525  		}
   526  		// If there is no remaining memory value, that means there was no memory update.
   527  		// Take any memory arg.
   528  		if lastmem[b.ID] == nil {
   529  			for _, v := range b.Values {
   530  				if v.Op == OpPhi {
   531  					continue
   532  				}
   533  				m := v.MemoryArg()
   534  				if m == nil {
   535  					continue
   536  				}
   537  				if lastmem[b.ID] != nil && lastmem[b.ID] != m {
   538  					f.Fatalf("two live memory values in %s: %s and %s", b, lastmem[b.ID], m)
   539  				}
   540  				lastmem[b.ID] = m
   541  			}
   542  		}
   543  	}
   544  	// Propagate last live memory through storeless blocks.
   545  	for {
   546  		changed := false
   547  		for _, b := range f.Blocks {
   548  			if lastmem[b.ID] != nil {
   549  				continue
   550  			}
   551  			for _, e := range b.Preds {
   552  				p := e.b
   553  				if lastmem[p.ID] != nil {
   554  					lastmem[b.ID] = lastmem[p.ID]
   555  					changed = true
   556  					break
   557  				}
   558  			}
   559  		}
   560  		if !changed {
   561  			break
   562  		}
   563  	}
   564  	// Check merge points.
   565  	for _, b := range f.Blocks {
   566  		for _, v := range b.Values {
   567  			if v.Op == OpPhi && v.Type.IsMemory() {
   568  				for i, a := range v.Args {
   569  					if a != lastmem[b.Preds[i].b.ID] {
   570  						f.Fatalf("inconsistent memory phi %s %d %s %s", v.LongString(), i, a, lastmem[b.Preds[i].b.ID])
   571  					}
   572  				}
   573  			}
   574  		}
   575  	}
   576  
   577  	// Check that only one memory is live at any point.
   578  	if f.scheduled {
   579  		for _, b := range f.Blocks {
   580  			var mem *Value // the current live memory in the block
   581  			for _, v := range b.Values {
   582  				if v.Op == OpPhi {
   583  					if v.Type.IsMemory() {
   584  						mem = v
   585  					}
   586  					continue
   587  				}
   588  				if mem == nil && len(b.Preds) > 0 {
   589  					// If no mem phi, take mem of any predecessor.
   590  					mem = lastmem[b.Preds[0].b.ID]
   591  				}
   592  				for _, a := range v.Args {
   593  					if a.Type.IsMemory() && a != mem {
   594  						f.Fatalf("two live mems @ %s: %s and %s", v, mem, a)
   595  					}
   596  				}
   597  				if v.Type.IsMemory() {
   598  					mem = v
   599  				}
   600  			}
   601  		}
   602  	}
   603  
   604  	// Check that after scheduling, phis are always first in the block.
   605  	if f.scheduled {
   606  		for _, b := range f.Blocks {
   607  			seenNonPhi := false
   608  			for _, v := range b.Values {
   609  				switch v.Op {
   610  				case OpPhi:
   611  					if seenNonPhi {
   612  						f.Fatalf("phi after non-phi @ %s: %s", b, v)
   613  					}
   614  				default:
   615  					seenNonPhi = true
   616  				}
   617  			}
   618  		}
   619  	}
   620  }
   621  
   622  // domCheck reports whether x dominates y (including x==y).
   623  func domCheck(f *Func, sdom SparseTree, x, y *Block) bool {
   624  	if !sdom.IsAncestorEq(f.Entry, y) {
   625  		// unreachable - ignore
   626  		return true
   627  	}
   628  	return sdom.IsAncestorEq(x, y)
   629  }
   630  
   631  // isExactFloat32 reports whether x can be exactly represented as a float32.
   632  func isExactFloat32(x float64) bool {
   633  	// Check the mantissa is in range.
   634  	if bits.TrailingZeros64(math.Float64bits(x)) < 52-23 {
   635  		return false
   636  	}
   637  	// Check the exponent is in range. The mantissa check above is sufficient for NaN values.
   638  	return math.IsNaN(x) || x == float64(float32(x))
   639  }
   640  

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