[PATCH] D51216: Fix IRBuilder.CreateFCmp(X, X) misfolding
Andrew Scheidecker via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Tue Feb 19 13:21:44 PST 2019
This revision was automatically updated to reflect the committed changes.
Closed by commit rL354381: [ConstantFold] Fix misfolding fcmp of a ConstantExpr NaN with itself. (authored by AndrewScheidecker, committed by ).
Changed prior to commit:
https://reviews.llvm.org/D51216?vs=186817&id=187436#toc
Repository:
rL LLVM
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D51216/new/
https://reviews.llvm.org/D51216
Files:
llvm/trunk/lib/IR/ConstantFold.cpp
llvm/trunk/test/Transforms/ConstProp/bitcast.ll
Index: llvm/trunk/test/Transforms/ConstProp/bitcast.ll
===================================================================
--- llvm/trunk/test/Transforms/ConstProp/bitcast.ll
+++ llvm/trunk/test/Transforms/ConstProp/bitcast.ll
@@ -36,21 +36,21 @@
ret i1 %cmp
}
-; FIXME: If the bitcasts result in a NaN FP value, then "ordered and equal" would be false.
+; Ensure that an "ordered and equal" fcmp of a ConstantExpr to itself is not folded, since the ConstantExpr may be a NaN.
define i1 @fcmp_constexpr_oeq(float %conv) {
; CHECK-LABEL: @fcmp_constexpr_oeq(
-; CHECK-NEXT: ret i1 true
+; CHECK-NEXT: ret i1 fcmp oeq (float bitcast (i32 ptrtoint (i16* @a to i32) to float), float bitcast (i32 ptrtoint (i16* @a to i32) to float))
;
%cmp = fcmp oeq float bitcast (i32 ptrtoint (i16* @a to i32) to float), bitcast (i32 ptrtoint (i16* @a to i32) to float)
ret i1 %cmp
}
-; FIXME: If the bitcasts result in a NaN FP value, then "unordered or not equal" would be true.
+; Ensure that an "unordered or not equal" fcmp of a ConstantExpr to itself is not folded, since the ConstantExpr may be a NaN.
define i1 @fcmp_constexpr_une(float %conv) {
; CHECK-LABEL: @fcmp_constexpr_une(
-; CHECK-NEXT: ret i1 false
+; CHECK-NEXT: ret i1 fcmp une (float bitcast (i32 ptrtoint (i16* @a to i32) to float), float bitcast (i32 ptrtoint (i16* @a to i32) to float))
;
%cmp = fcmp une float bitcast (i32 ptrtoint (i16* @a to i32) to float), bitcast (i32 ptrtoint (i16* @a to i32) to float)
ret i1 %cmp
Index: llvm/trunk/lib/IR/ConstantFold.cpp
===================================================================
--- llvm/trunk/lib/IR/ConstantFold.cpp
+++ llvm/trunk/lib/IR/ConstantFold.cpp
@@ -1359,8 +1359,9 @@
assert(V1->getType() == V2->getType() &&
"Cannot compare values of different types!");
- // Handle degenerate case quickly
- if (V1 == V2) return FCmpInst::FCMP_OEQ;
+ // We do not know if a constant expression will evaluate to a number or NaN.
+ // Therefore, we can only say that the relation is unordered or equal.
+ if (V1 == V2) return FCmpInst::FCMP_UEQ;
if (!isa<ConstantExpr>(V1)) {
if (!isa<ConstantExpr>(V2)) {
@@ -1855,7 +1856,6 @@
default: llvm_unreachable("Unknown relation!");
case FCmpInst::FCMP_UNO:
case FCmpInst::FCMP_ORD:
- case FCmpInst::FCMP_UEQ:
case FCmpInst::FCMP_UNE:
case FCmpInst::FCMP_ULT:
case FCmpInst::FCMP_UGT:
@@ -1901,6 +1901,13 @@
else if (pred == FCmpInst::FCMP_ONE || pred == FCmpInst::FCMP_UNE)
Result = 1;
break;
+ case FCmpInst::FCMP_UEQ: // We know that C1 == C2 || isUnordered(C1, C2).
+ // We can only partially decide this relation.
+ if (pred == FCmpInst::FCMP_ONE)
+ Result = 0;
+ else if (pred == FCmpInst::FCMP_UEQ)
+ Result = 1;
+ break;
}
// If we evaluated the result, return it now.
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