ConstantFolding: Fix handling of canonicalize for ppc_fp128 0s

[jcranmer-intel]

This strikes me as correct, but I would prefer someone more expert in PowerPC specifically to comment on this.

[arsenm]

ping

[arsenm]

ping

[qiucf]

LGTM. Thanks.

[arsenm]

4fa54f8b8196e83c7ab8856dab582387ce07282f

llvm/lib/Analysis/ConstantFolding.cpp

if (!ORM || *ORM == RoundingMode::Dynamic)
     return RoundingMode::NearestTiesToEven;
   return *ORM;
 }
 
 /// Try to constant fold llvm.canonicalize for the given caller and value.
 static Constant *constantFoldCanonicalize(const Type *Ty, const CallBase *CI,
                                           const APFloat &Src) {
   // Zero, positive and negative, is always OK to fold.
-  if (Src.isZero())
-    return ConstantFP::get(CI->getContext(), Src);
+  if (Src.isZero()) {
+    // Get a fresh 0, since ppc_fp128 does have non-canonical zeros.
+    return ConstantFP::get(
+        CI->getContext(),
+        APFloat::getZero(Src.getSemantics(), Src.isNegative()));
+  }
 
   if (!Ty->isIEEELikeFPTy())
     return nullptr;
 
   // Zero is always canonical and the sign must be preserved.
   //
   // Denorms and nans may have special encodings, but it should be OK to fold a
   // totally average number.

llvm/test/Transforms/InstSimplify/canonicalize.ll

 define ppc_fp128 @canonicalize_negzero_ppcf128() {
 ; CHECK-LABEL: @canonicalize_negzero_ppcf128(
 ; CHECK-NEXT:    ret ppc_fp128 0xM80000000000000000000000000000000
 ;
   %ret = call ppc_fp128 @llvm.canonicalize.ppcf128(ppc_fp128 0xM80000000000000000000000000000000)
   ret ppc_fp128 %ret
 }
 
+define ppc_fp128 @canonicalize_noncanonical_zero_0_ppcf128() {
+; CHECK-LABEL: @canonicalize_noncanonical_zero_0_ppcf128(
+; CHECK-NEXT:    ret ppc_fp128 0xM00000000000000000000000000000000
+;
+  %ret = call ppc_fp128 @llvm.canonicalize.ppcf128(ppc_fp128 0xM0000000000000000ffffffffffffffff)
+  ret ppc_fp128 %ret
+}
+
+define ppc_fp128 @canonicalize_noncanonical_zero_1_ppcf128() {
+; CHECK-LABEL: @canonicalize_noncanonical_zero_1_ppcf128(
+; CHECK-NEXT:    ret ppc_fp128 0xM00000000000000000000000000000000
+;
+  %ret = call ppc_fp128 @llvm.canonicalize.ppcf128(ppc_fp128 0xM00000000000000000000000000000001)
+  ret ppc_fp128 %ret
+}
+
+define ppc_fp128 @canonicalize_noncanonical_negzero_0_ppcf128() {
+; CHECK-LABEL: @canonicalize_noncanonical_negzero_0_ppcf128(
+; CHECK-NEXT:    ret ppc_fp128 0xM80000000000000000000000000000000
+;
+  %ret = call ppc_fp128 @llvm.canonicalize.ppcf128(ppc_fp128 0xM8000000000000000ffffffffffffffff)
+  ret ppc_fp128 %ret
+}
+
 define ppc_fp128 @canonicalize_inf_ppcf128() {
 ; CHECK-LABEL: @canonicalize_inf_ppcf128(
 ; CHECK-NEXT:    [[RET:%.*]] = call ppc_fp128 @llvm.canonicalize.ppcf128(ppc_fp128 0xM7FF00000000000000000000000000000)
 ; CHECK-NEXT:    ret ppc_fp128 [[RET]]
 ;
   %ret = call ppc_fp128 @llvm.canonicalize.ppcf128(ppc_fp128 0xM7FF00000000000000000000000000000)
   ret ppc_fp128 %ret
 }