Revert "cmd/compile/internal: merge stack slots for selected local auto vars"

This reverts CL 553055.

Reason for revert: causes crypto/ecdsa failures on linux ppc64/s390x builders

Change-Id: I9266b030693a5b6b1e667a009de89d613755b048
Reviewed-on: https://go-review.googlesource.com/c/go/+/575236
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Than McIntosh <[email protected]>
Auto-Submit: Than McIntosh <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: cuonglm

src/cmd/compile/internal/base/debug.go

@@ -41,10 +41,6 @@ type DebugFlags struct {
 	LoopVarHash           string `help:"for debugging changes in loop behavior. Overrides experiment and loopvar flag."`
 	LocationLists         int    `help:"print information about DWARF location list creation"`
 	MaxShapeLen           int    `help:"hash shape names longer than this threshold (default 500)" concurrent:"ok"`
-	MergeLocals           int    `help:"merge together non-interfering local stack slots" concurrent:"ok"`
-	MergeLocalsDumpFunc   string `help:"dump specified func in merge locals"`
-	MergeLocalsHash       string `help:"hash value for debugging stack slot merging of local variables" concurrent:"ok"`
-	MergeLocalsTrace      int    `help:"trace debug output for locals merging"`
 	Nil                   int    `help:"print information about nil checks"`
 	NoOpenDefer           int    `help:"disable open-coded defers" concurrent:"ok"`
 	NoRefName             int    `help:"do not include referenced symbol names in object file" concurrent:"ok"`

src/cmd/compile/internal/base/flag.go

@@ -184,7 +184,6 @@ func ParseFlags() {
 	Debug.SyncFrames = -1 // disable sync markers by default
 	Debug.ZeroCopy = 1
 	Debug.RangeFuncCheck = 1
-	Debug.MergeLocals = 1
 
 	Debug.Checkptr = -1 // so we can tell whether it is set explicitly
 
@@ -261,9 +260,6 @@ func ParseFlags() {
 	if Debug.PGOHash != "" {
 		PGOHash = NewHashDebug("pgohash", Debug.PGOHash, nil)
 	}
-	if Debug.MergeLocalsHash != "" {
-		MergeLocalsHash = NewHashDebug("mergelocals", Debug.MergeLocalsHash, nil)
-	}
 
 	if Flag.MSan && !platform.MSanSupported(buildcfg.GOOS, buildcfg.GOARCH) {
 		log.Fatalf("%s/%s does not support -msan", buildcfg.GOOS, buildcfg.GOARCH)

src/cmd/compile/internal/base/hashdebug.go

@@ -53,10 +53,9 @@ func (d *HashDebug) SetInlineSuffixOnly(b bool) *HashDebug {
 // The default compiler-debugging HashDebug, for "-d=gossahash=..."
 var hashDebug *HashDebug
 
-var FmaHash *HashDebug         // for debugging fused-multiply-add floating point changes
-var LoopVarHash *HashDebug     // for debugging shared/private loop variable changes
-var PGOHash *HashDebug         // for debugging PGO optimization decisions
-var MergeLocalsHash *HashDebug // for debugging local stack slot merging changes
+var FmaHash *HashDebug     // for debugging fused-multiply-add floating point changes
+var LoopVarHash *HashDebug // for debugging shared/private loop variable changes
+var PGOHash *HashDebug     // for debugging PGO optimization decisions
 
 // DebugHashMatchPkgFunc reports whether debug variable Gossahash
 //

src/cmd/compile/internal/ir/name.go

@@ -194,7 +194,6 @@ const (
 	nameLibfuzzer8BitCounter     // if PEXTERN should be assigned to __sancov_cntrs section
 	nameCoverageAuxVar           // instrumentation counter var or pkg ID for cmd/cover
 	nameAlias                    // is type name an alias
-	nameNonMergeable             // not a candidate for stack slot merging
 )
 
 func (n *Name) Readonly() bool                 { return n.flags&nameReadonly != 0 }
@@ -210,7 +209,6 @@ func (n *Name) InlLocal() bool                 { return n.flags&nameInlLocal !=
 func (n *Name) OpenDeferSlot() bool            { return n.flags&nameOpenDeferSlot != 0 }
 func (n *Name) Libfuzzer8BitCounter() bool     { return n.flags&nameLibfuzzer8BitCounter != 0 }
 func (n *Name) CoverageAuxVar() bool           { return n.flags&nameCoverageAuxVar != 0 }
-func (n *Name) NonMergeable() bool             { return n.flags&nameNonMergeable != 0 }
 
 func (n *Name) setReadonly(b bool)                 { n.flags.set(nameReadonly, b) }
 func (n *Name) SetNeedzero(b bool)                 { n.flags.set(nameNeedzero, b) }
@@ -225,7 +223,6 @@ func (n *Name) SetInlLocal(b bool)                 { n.flags.set(nameInlLocal, b
 func (n *Name) SetOpenDeferSlot(b bool)            { n.flags.set(nameOpenDeferSlot, b) }
 func (n *Name) SetLibfuzzer8BitCounter(b bool)     { n.flags.set(nameLibfuzzer8BitCounter, b) }
 func (n *Name) SetCoverageAuxVar(b bool)           { n.flags.set(nameCoverageAuxVar, b) }
-func (n *Name) SetNonMergeable(b bool)             { n.flags.set(nameNonMergeable, b) }
 
 // OnStack reports whether variable n may reside on the stack.
 func (n *Name) OnStack() bool {