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

Documentation: cmd/compile/internal/ssa

     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:
   149  				canHaveAuxInt = true
   150  			case auxInt128:
   151  				// AuxInt must be zero, so leave canHaveAuxInt set to false.
   152  			case auxUInt8:
   153  				if v.AuxInt != int64(uint8(v.AuxInt)) {
   154  					f.Fatalf("bad uint8 AuxInt value for %v", v)
   155  				}
   156  				canHaveAuxInt = true
   157  			case auxFloat32:
   158  				canHaveAuxInt = true
   159  				if math.IsNaN(v.AuxFloat()) {
   160  					f.Fatalf("value %v has an AuxInt that encodes a NaN", v)
   161  				}
   162  				if !isExactFloat32(v.AuxFloat()) {
   163  					f.Fatalf("value %v has an AuxInt value that is not an exact float32", v)
   164  				}
   165  			case auxFloat64:
   166  				canHaveAuxInt = true
   167  				if math.IsNaN(v.AuxFloat()) {
   168  					f.Fatalf("value %v has an AuxInt that encodes a NaN", v)
   169  				}
   170  			case auxString:
   171  				if _, ok := v.Aux.(stringAux); !ok {
   172  					f.Fatalf("value %v has Aux type %T, want string", v, v.Aux)
   173  				}
   174  				canHaveAux = true
   175  			case auxCallOff:
   176  				canHaveAuxInt = true
   177  				fallthrough
   178  			case auxCall:
   179  				if ac, ok := v.Aux.(*AuxCall); ok {
   180  					if v.Op == OpStaticCall && ac.Fn == nil {
   181  						f.Fatalf("value %v has *AuxCall with nil Fn", v)
   182  					}
   183  				} else {
   184  					f.Fatalf("value %v has Aux type %T, want *AuxCall", v, v.Aux)
   185  				}
   186  				canHaveAux = true
   187  			case auxNameOffsetInt8:
   188  				if _, ok := v.Aux.(*AuxNameOffset); !ok {
   189  					f.Fatalf("value %v has Aux type %T, want *AuxNameOffset", v, v.Aux)
   190  				}
   191  				canHaveAux = true
   192  				canHaveAuxInt = true
   193  			case auxSym, auxTyp:
   194  				canHaveAux = true
   195  			case auxSymOff, auxSymValAndOff, auxTypSize:
   196  				canHaveAuxInt = true
   197  				canHaveAux = true
   198  			case auxCCop:
   199  				if opcodeTable[Op(v.AuxInt)].name == "OpInvalid" {
   200  					f.Fatalf("value %v has an AuxInt value that is a valid opcode", v)
   201  				}
   202  				canHaveAuxInt = true
   203  			case auxS390XCCMask:
   204  				if _, ok := v.Aux.(s390x.CCMask); !ok {
   205  					f.Fatalf("bad type %T for S390XCCMask in %v", v.Aux, v)
   206  				}
   207  				canHaveAux = true
   208  			case auxS390XRotateParams:
   209  				if _, ok := v.Aux.(s390x.RotateParams); !ok {
   210  					f.Fatalf("bad type %T for S390XRotateParams in %v", v.Aux, v)
   211  				}
   212  				canHaveAux = true
   213  			case auxFlagConstant:
   214  				if v.AuxInt < 0 || v.AuxInt > 15 {
   215  					f.Fatalf("bad FlagConstant AuxInt value for %v", v)
   216  				}
   217  				canHaveAuxInt = true
   218  			default:
   219  				f.Fatalf("unknown aux type for %s", v.Op)
   220  			}
   221  			if !canHaveAux && v.Aux != nil {
   222  				f.Fatalf("value %s has an Aux value %v but shouldn't", v.LongString(), v.Aux)
   223  			}
   224  			if !canHaveAuxInt && v.AuxInt != 0 {
   225  				f.Fatalf("value %s has an AuxInt value %d but shouldn't", v.LongString(), v.AuxInt)
   226  			}
   227  
   228  			for i, arg := range v.Args {
   229  				if arg == nil {
   230  					f.Fatalf("value %s has nil arg", v.LongString())
   231  				}
   232  				if v.Op != OpPhi {
   233  					// For non-Phi ops, memory args must be last, if present
   234  					if arg.Type.IsMemory() && i != len(v.Args)-1 {
   235  						f.Fatalf("value %s has non-final memory arg (%d < %d)", v.LongString(), i, len(v.Args)-1)
   236  					}
   237  				}
   238  			}
   239  
   240  			if valueMark[v.ID] {
   241  				f.Fatalf("value %s appears twice!", v.LongString())
   242  			}
   243  			valueMark[v.ID] = true
   244  
   245  			if v.Block != b {
   246  				f.Fatalf("%s.block != %s", v, b)
   247  			}
   248  			if v.Op == OpPhi && len(v.Args) != len(b.Preds) {
   249  				f.Fatalf("phi length %s does not match pred length %d for block %s", v.LongString(), len(b.Preds), b)
   250  			}
   251  
   252  			if v.Op == OpAddr {
   253  				if len(v.Args) == 0 {
   254  					f.Fatalf("no args for OpAddr %s", v.LongString())
   255  				}
   256  				if v.Args[0].Op != OpSB {
   257  					f.Fatalf("bad arg to OpAddr %v", v)
   258  				}
   259  			}
   260  
   261  			if v.Op == OpLocalAddr {
   262  				if len(v.Args) != 2 {
   263  					f.Fatalf("wrong # of args for OpLocalAddr %s", v.LongString())
   264  				}
   265  				if v.Args[0].Op != OpSP {
   266  					f.Fatalf("bad arg 0 to OpLocalAddr %v", v)
   267  				}
   268  				if !v.Args[1].Type.IsMemory() {
   269  					f.Fatalf("bad arg 1 to OpLocalAddr %v", v)
   270  				}
   271  			}
   272  
   273  			if f.RegAlloc != nil && f.Config.SoftFloat && v.Type.IsFloat() {
   274  				f.Fatalf("unexpected floating-point type %v", v.LongString())
   275  			}
   276  
   277  			// Check types.
   278  			// TODO: more type checks?
   279  			switch c := f.Config; v.Op {
   280  			case OpSP, OpSB:
   281  				if v.Type != c.Types.Uintptr {
   282  					f.Fatalf("bad %s type: want uintptr, have %s",
   283  						v.Op, v.Type.String())
   284  				}
   285  			case OpStringLen:
   286  				if v.Type != c.Types.Int {
   287  					f.Fatalf("bad %s type: want int, have %s",
   288  						v.Op, v.Type.String())
   289  				}
   290  			case OpLoad:
   291  				if !v.Args[1].Type.IsMemory() {
   292  					f.Fatalf("bad arg 1 type to %s: want mem, have %s",
   293  						v.Op, v.Args[1].Type.String())
   294  				}
   295  			case OpStore:
   296  				if !v.Type.IsMemory() {
   297  					f.Fatalf("bad %s type: want mem, have %s",
   298  						v.Op, v.Type.String())
   299  				}
   300  				if !v.Args[2].Type.IsMemory() {
   301  					f.Fatalf("bad arg 2 type to %s: want mem, have %s",
   302  						v.Op, v.Args[2].Type.String())
   303  				}
   304  			case OpCondSelect:
   305  				if !v.Args[2].Type.IsBoolean() {
   306  					f.Fatalf("bad arg 2 type to %s: want boolean, have %s",
   307  						v.Op, v.Args[2].Type.String())
   308  				}
   309  			case OpAddPtr:
   310  				if !v.Args[0].Type.IsPtrShaped() && v.Args[0].Type != c.Types.Uintptr {
   311  					f.Fatalf("bad arg 0 type to %s: want ptr, have %s", v.Op, v.Args[0].LongString())
   312  				}
   313  				if !v.Args[1].Type.IsInteger() {
   314  					f.Fatalf("bad arg 1 type to %s: want integer, have %s", v.Op, v.Args[1].LongString())
   315  				}
   316  			case OpVarDef:
   317  				n := v.Aux.(*ir.Name)
   318  				if !n.Type().HasPointers() && !IsMergeCandidate(n) {
   319  					f.Fatalf("vardef must be merge candidate or have pointer type %s", v.Aux.(*ir.Name).Type().String())
   320  				}
   321  			case OpNilCheck:
   322  				// nil checks have pointer type before scheduling, and
   323  				// void type after scheduling.
   324  				if f.scheduled {
   325  					if v.Uses != 0 {
   326  						f.Fatalf("nilcheck must have 0 uses %s", v.Uses)
   327  					}
   328  					if !v.Type.IsVoid() {
   329  						f.Fatalf("nilcheck must have void type %s", v.Type.String())
   330  					}
   331  				} else {
   332  					if !v.Type.IsPtrShaped() && !v.Type.IsUintptr() {
   333  						f.Fatalf("nilcheck must have pointer type %s", v.Type.String())
   334  					}
   335  				}
   336  				if !v.Args[0].Type.IsPtrShaped() && !v.Args[0].Type.IsUintptr() {
   337  					f.Fatalf("nilcheck must have argument of pointer type %s", v.Args[0].Type.String())
   338  				}
   339  				if !v.Args[1].Type.IsMemory() {
   340  					f.Fatalf("bad arg 1 type to %s: want mem, have %s",
   341  						v.Op, v.Args[1].Type.String())
   342  				}
   343  			}
   344  
   345  			// TODO: check for cycles in values
   346  		}
   347  	}
   348  
   349  	// Check to make sure all Blocks referenced are in the function.
   350  	if !blockMark[f.Entry.ID] {
   351  		f.Fatalf("entry block %v is missing", f.Entry)
   352  	}
   353  	for _, b := range f.Blocks {
   354  		for _, c := range b.Preds {
   355  			if !blockMark[c.b.ID] {
   356  				f.Fatalf("predecessor block %v for %v is missing", c, b)
   357  			}
   358  		}
   359  		for _, c := range b.Succs {
   360  			if !blockMark[c.b.ID] {
   361  				f.Fatalf("successor block %v for %v is missing", c, b)
   362  			}
   363  		}
   364  	}
   365  
   366  	if len(f.Entry.Preds) > 0 {
   367  		f.Fatalf("entry block %s of %s has predecessor(s) %v", f.Entry, f.Name, f.Entry.Preds)
   368  	}
   369  
   370  	// Check to make sure all Values referenced are in the function.
   371  	for _, b := range f.Blocks {
   372  		for _, v := range b.Values {
   373  			for i, a := range v.Args {
   374  				if !valueMark[a.ID] {
   375  					f.Fatalf("%v, arg %d of %s, is missing", a, i, v.LongString())
   376  				}
   377  			}
   378  		}
   379  		for _, c := range b.ControlValues() {
   380  			if !valueMark[c.ID] {
   381  				f.Fatalf("control value for %s is missing: %v", b, c)
   382  			}
   383  		}
   384  	}
   385  	for b := f.freeBlocks; b != nil; b = b.succstorage[0].b {
   386  		if blockMark[b.ID] {
   387  			f.Fatalf("used block b%d in free list", b.ID)
   388  		}
   389  	}
   390  	for v := f.freeValues; v != nil; v = v.argstorage[0] {
   391  		if valueMark[v.ID] {
   392  			f.Fatalf("used value v%d in free list", v.ID)
   393  		}
   394  	}
   395  
   396  	// Check to make sure all args dominate uses.
   397  	if f.RegAlloc == nil {
   398  		// Note: regalloc introduces non-dominating args.
   399  		// See TODO in regalloc.go.
   400  		sdom := f.Sdom()
   401  		for _, b := range f.Blocks {
   402  			for _, v := range b.Values {
   403  				for i, arg := range v.Args {
   404  					x := arg.Block
   405  					y := b
   406  					if v.Op == OpPhi {
   407  						y = b.Preds[i].b
   408  					}
   409  					if !domCheck(f, sdom, x, y) {
   410  						f.Fatalf("arg %d of value %s does not dominate, arg=%s", i, v.LongString(), arg.LongString())
   411  					}
   412  				}
   413  			}
   414  			for _, c := range b.ControlValues() {
   415  				if !domCheck(f, sdom, c.Block, b) {
   416  					f.Fatalf("control value %s for %s doesn't dominate", c, b)
   417  				}
   418  			}
   419  		}
   420  	}
   421  
   422  	// Check loop construction
   423  	if f.RegAlloc == nil && f.pass != nil { // non-nil pass allows better-targeted debug printing
   424  		ln := f.loopnest()
   425  		if !ln.hasIrreducible {
   426  			po := f.postorder() // use po to avoid unreachable blocks.
   427  			for _, b := range po {
   428  				for _, s := range b.Succs {
   429  					bb := s.Block()
   430  					if ln.b2l[b.ID] == nil && ln.b2l[bb.ID] != nil && bb != ln.b2l[bb.ID].header {
   431  						f.Fatalf("block %s not in loop branches to non-header block %s in loop", b.String(), bb.String())
   432  					}
   433  					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]) {
   434  						f.Fatalf("block %s in loop branches to non-header block %s in non-containing loop", b.String(), bb.String())
   435  					}
   436  				}
   437  			}
   438  		}
   439  	}
   440  
   441  	// Check use counts
   442  	uses := make([]int32, f.NumValues())
   443  	for _, b := range f.Blocks {
   444  		for _, v := range b.Values {
   445  			for _, a := range v.Args {
   446  				uses[a.ID]++
   447  			}
   448  		}
   449  		for _, c := range b.ControlValues() {
   450  			uses[c.ID]++
   451  		}
   452  	}
   453  	for _, b := range f.Blocks {
   454  		for _, v := range b.Values {
   455  			if v.Uses != uses[v.ID] {
   456  				f.Fatalf("%s has %d uses, but has Uses=%d", v, uses[v.ID], v.Uses)
   457  			}
   458  		}
   459  	}
   460  
   461  	memCheck(f)
   462  }
   463  
   464  func memCheck(f *Func) {
   465  	// Check that if a tuple has a memory type, it is second.
   466  	for _, b := range f.Blocks {
   467  		for _, v := range b.Values {
   468  			if v.Type.IsTuple() && v.Type.FieldType(0).IsMemory() {
   469  				f.Fatalf("memory is first in a tuple: %s\n", v.LongString())
   470  			}
   471  		}
   472  	}
   473  
   474  	// Single live memory checks.
   475  	// These checks only work if there are no memory copies.
   476  	// (Memory copies introduce ambiguity about which mem value is really live.
   477  	// probably fixable, but it's easier to avoid the problem.)
   478  	// For the same reason, disable this check if some memory ops are unused.
   479  	for _, b := range f.Blocks {
   480  		for _, v := range b.Values {
   481  			if (v.Op == OpCopy || v.Uses == 0) && v.Type.IsMemory() {
   482  				return
   483  			}
   484  		}
   485  		if b != f.Entry && len(b.Preds) == 0 {
   486  			return
   487  		}
   488  	}
   489  
   490  	// Compute live memory at the end of each block.
   491  	lastmem := make([]*Value, f.NumBlocks())
   492  	ss := newSparseSet(f.NumValues())
   493  	for _, b := range f.Blocks {
   494  		// Mark overwritten memory values. Those are args of other
   495  		// ops that generate memory values.
   496  		ss.clear()
   497  		for _, v := range b.Values {
   498  			if v.Op == OpPhi || !v.Type.IsMemory() {
   499  				continue
   500  			}
   501  			if m := v.MemoryArg(); m != nil {
   502  				ss.add(m.ID)
   503  			}
   504  		}
   505  		// There should be at most one remaining unoverwritten memory value.
   506  		for _, v := range b.Values {
   507  			if !v.Type.IsMemory() {
   508  				continue
   509  			}
   510  			if ss.contains(v.ID) {
   511  				continue
   512  			}
   513  			if lastmem[b.ID] != nil {
   514  				f.Fatalf("two live memory values in %s: %s and %s", b, lastmem[b.ID], v)
   515  			}
   516  			lastmem[b.ID] = v
   517  		}
   518  		// If there is no remaining memory value, that means there was no memory update.
   519  		// Take any memory arg.
   520  		if lastmem[b.ID] == nil {
   521  			for _, v := range b.Values {
   522  				if v.Op == OpPhi {
   523  					continue
   524  				}
   525  				m := v.MemoryArg()
   526  				if m == nil {
   527  					continue
   528  				}
   529  				if lastmem[b.ID] != nil && lastmem[b.ID] != m {
   530  					f.Fatalf("two live memory values in %s: %s and %s", b, lastmem[b.ID], m)
   531  				}
   532  				lastmem[b.ID] = m
   533  			}
   534  		}
   535  	}
   536  	// Propagate last live memory through storeless blocks.
   537  	for {
   538  		changed := false
   539  		for _, b := range f.Blocks {
   540  			if lastmem[b.ID] != nil {
   541  				continue
   542  			}
   543  			for _, e := range b.Preds {
   544  				p := e.b
   545  				if lastmem[p.ID] != nil {
   546  					lastmem[b.ID] = lastmem[p.ID]
   547  					changed = true
   548  					break
   549  				}
   550  			}
   551  		}
   552  		if !changed {
   553  			break
   554  		}
   555  	}
   556  	// Check merge points.
   557  	for _, b := range f.Blocks {
   558  		for _, v := range b.Values {
   559  			if v.Op == OpPhi && v.Type.IsMemory() {
   560  				for i, a := range v.Args {
   561  					if a != lastmem[b.Preds[i].b.ID] {
   562  						f.Fatalf("inconsistent memory phi %s %d %s %s", v.LongString(), i, a, lastmem[b.Preds[i].b.ID])
   563  					}
   564  				}
   565  			}
   566  		}
   567  	}
   568  
   569  	// Check that only one memory is live at any point.
   570  	if f.scheduled {
   571  		for _, b := range f.Blocks {
   572  			var mem *Value // the current live memory in the block
   573  			for _, v := range b.Values {
   574  				if v.Op == OpPhi {
   575  					if v.Type.IsMemory() {
   576  						mem = v
   577  					}
   578  					continue
   579  				}
   580  				if mem == nil && len(b.Preds) > 0 {
   581  					// If no mem phi, take mem of any predecessor.
   582  					mem = lastmem[b.Preds[0].b.ID]
   583  				}
   584  				for _, a := range v.Args {
   585  					if a.Type.IsMemory() && a != mem {
   586  						f.Fatalf("two live mems @ %s: %s and %s", v, mem, a)
   587  					}
   588  				}
   589  				if v.Type.IsMemory() {
   590  					mem = v
   591  				}
   592  			}
   593  		}
   594  	}
   595  
   596  	// Check that after scheduling, phis are always first in the block.
   597  	if f.scheduled {
   598  		for _, b := range f.Blocks {
   599  			seenNonPhi := false
   600  			for _, v := range b.Values {
   601  				switch v.Op {
   602  				case OpPhi:
   603  					if seenNonPhi {
   604  						f.Fatalf("phi after non-phi @ %s: %s", b, v)
   605  					}
   606  				default:
   607  					seenNonPhi = true
   608  				}
   609  			}
   610  		}
   611  	}
   612  }
   613  
   614  // domCheck reports whether x dominates y (including x==y).
   615  func domCheck(f *Func, sdom SparseTree, x, y *Block) bool {
   616  	if !sdom.IsAncestorEq(f.Entry, y) {
   617  		// unreachable - ignore
   618  		return true
   619  	}
   620  	return sdom.IsAncestorEq(x, y)
   621  }
   622  
   623  // isExactFloat32 reports whether x can be exactly represented as a float32.
   624  func isExactFloat32(x float64) bool {
   625  	// Check the mantissa is in range.
   626  	if bits.TrailingZeros64(math.Float64bits(x)) < 52-23 {
   627  		return false
   628  	}
   629  	// Check the exponent is in range. The mantissa check above is sufficient for NaN values.
   630  	return math.IsNaN(x) || x == float64(float32(x))
   631  }
   632  

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