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signed-zero bug in LLVM 3.6.0
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Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,103 @@ | ||
diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp | ||
index 4a85780..73a1f25 100644 | ||
--- a/lib/Transforms/Scalar/GVN.cpp | ||
+++ b/lib/Transforms/Scalar/GVN.cpp | ||
@@ -2182,12 +2182,16 @@ bool GVN::propagateEquality(Value *LHS, Value *RHS, | ||
// Handle the floating point versions of equality comparisons too. | ||
if ((isKnownTrue && Cmp->getPredicate() == CmpInst::FCMP_OEQ) || | ||
(isKnownFalse && Cmp->getPredicate() == CmpInst::FCMP_UNE)) { | ||
- // Floating point -0.0 and 0.0 compare equal, so we can't | ||
- // propagate a constant based on that comparison. | ||
+ | ||
+ // Floating point -0.0 and 0.0 compare equal, so we can only | ||
+ // propagate values if we know that we have a constant and that | ||
+ // its value is non-zero. | ||
+ | ||
// FIXME: We should do this optimization if 'no signed zeros' is | ||
// applicable via an instruction-level fast-math-flag or some other | ||
// indicator that relaxed FP semantics are being used. | ||
- if (!isa<ConstantFP>(Op1) || !cast<ConstantFP>(Op1)->isZero()) | ||
+ | ||
+ if (isa<ConstantFP>(Op1) && !cast<ConstantFP>(Op1)->isZero()) | ||
Worklist.push_back(std::make_pair(Op0, Op1)); | ||
} | ||
|
||
diff --git a/test/Transforms/GVN/edge.ll b/test/Transforms/GVN/edge.ll | ||
index f28a76b..0c1a3fb 100644 | ||
--- a/test/Transforms/GVN/edge.ll | ||
+++ b/test/Transforms/GVN/edge.ll | ||
@@ -59,7 +59,7 @@ bb2: | ||
ret void | ||
} | ||
|
||
-define double @fcmp_oeq(double %x, double %y) { | ||
+define double @fcmp_oeq_not_zero(double %x, double %y) { | ||
entry: | ||
%cmp = fcmp oeq double %y, 2.0 | ||
br i1 %cmp, label %if, label %return | ||
@@ -72,11 +72,11 @@ return: | ||
%retval = phi double [ %div, %if ], [ %x, %entry ] | ||
ret double %retval | ||
|
||
-; CHECK-LABEL: define double @fcmp_oeq( | ||
+; CHECK-LABEL: define double @fcmp_oeq_not_zero( | ||
; CHECK: %div = fdiv double %x, 2.0 | ||
} | ||
|
||
-define double @fcmp_une(double %x, double %y) { | ||
+define double @fcmp_une_not_zero(double %x, double %y) { | ||
entry: | ||
%cmp = fcmp une double %y, 2.0 | ||
br i1 %cmp, label %return, label %else | ||
@@ -89,7 +89,7 @@ return: | ||
%retval = phi double [ %div, %else ], [ %x, %entry ] | ||
ret double %retval | ||
|
||
-; CHECK-LABEL: define double @fcmp_une( | ||
+; CHECK-LABEL: define double @fcmp_une_not_zero( | ||
; CHECK: %div = fdiv double %x, 2.0 | ||
} | ||
|
||
@@ -129,3 +129,42 @@ return: | ||
; CHECK-LABEL: define double @fcmp_une_zero( | ||
; CHECK: %div = fdiv double %x, %y | ||
} | ||
+ | ||
+; We also cannot propagate a value if it's not a constant. | ||
+; This is because the value could be 0.0 or -0.0. | ||
+ | ||
+define double @fcmp_oeq_maybe_zero(double %x, double %y, double %z1, double %z2) { | ||
+entry: | ||
+ %z = fadd double %z1, %z2 | ||
+ %cmp = fcmp oeq double %y, %z | ||
+ br i1 %cmp, label %if, label %return | ||
+ | ||
+if: | ||
+ %div = fdiv double %x, %z | ||
+ br label %return | ||
+ | ||
+return: | ||
+ %retval = phi double [ %div, %if ], [ %x, %entry ] | ||
+ ret double %retval | ||
+ | ||
+; CHECK-LABEL: define double @fcmp_oeq_maybe_zero( | ||
+; CHECK: %div = fdiv double %x, %z | ||
+} | ||
+ | ||
+define double @fcmp_une_maybe_zero(double %x, double %y, double %z1, double %z2) { | ||
+entry: | ||
+ %z = fadd double %z1, %z2 | ||
+ %cmp = fcmp une double %y, %z | ||
+ br i1 %cmp, label %return, label %else | ||
+ | ||
+else: | ||
+ %div = fdiv double %x, %z | ||
+ br label %return | ||
+ | ||
+return: | ||
+ %retval = phi double [ %div, %else ], [ %x, %entry ] | ||
+ ret double %retval | ||
+ | ||
+; CHECK-LABEL: define double @fcmp_une_maybe_zero( | ||
+; CHECK: %div = fdiv double %x, %z | ||
+} |