[llvm] r261813 - IR: Make the X / undef -> undef fold match the comment
Justin Bogner via llvm-commits
llvm-commits at lists.llvm.org
Wed Feb 24 17:02:19 PST 2016
Author: bogner
Date: Wed Feb 24 19:02:18 2016
New Revision: 261813
URL: http://llvm.org/viewvc/llvm-project?rev=261813&view=rev
Log:
IR: Make the X / undef -> undef fold match the comment
The constant folding for sdiv and udiv has a big discrepancy between the
comments and the code, which looks like a typo. Currently, we're folding
X / undef pretty inconsistently:
0 / undef -> undef
C / undef -> 0
undef / undef -> 0
Whereas the comments state we do X / undef -> undef. The logic that
returns zero is actually commented as doing undef / X -> 0, despite that
the LHS isn't undef in many of the cases that hit it.
Modified:
llvm/trunk/lib/IR/ConstantFold.cpp
llvm/trunk/test/Transforms/InstSimplify/undef.ll
Modified: llvm/trunk/lib/IR/ConstantFold.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/ConstantFold.cpp?rev=261813&r1=261812&r2=261813&view=diff
==============================================================================
--- llvm/trunk/lib/IR/ConstantFold.cpp (original)
+++ llvm/trunk/lib/IR/ConstantFold.cpp Wed Feb 24 19:02:18 2016
@@ -948,7 +948,7 @@ Constant *llvm::ConstantFoldBinaryInstru
case Instruction::SDiv:
case Instruction::UDiv:
// X / undef -> undef
- if (match(C1, m_Zero()))
+ if (isa<UndefValue>(C2))
return C2;
// undef / 0 -> undef
// undef / 1 -> undef
Modified: llvm/trunk/test/Transforms/InstSimplify/undef.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstSimplify/undef.ll?rev=261813&r1=261812&r2=261813&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstSimplify/undef.ll (original)
+++ llvm/trunk/test/Transforms/InstSimplify/undef.ll Wed Feb 24 19:02:18 2016
@@ -279,3 +279,24 @@ define i32 @test36(i32 %V) {
%b = extractelement <4 x i32> undef, i32 %V
ret i32 %b
}
+
+; CHECK-LABEL: @test37
+; CHECK: ret i32 undef
+define i32 @test37() {
+ %b = udiv i32 undef, undef
+ ret i32 %b
+}
+
+; CHECK-LABEL: @test38
+; CHECK: ret i32 undef
+define i32 @test38(i32 %a) {
+ %b = udiv i32 %a, undef
+ ret i32 %b
+}
+
+; CHECK-LABEL: @test39
+; CHECK: ret i32 undef
+define i32 @test39() {
+ %b = udiv i32 0, undef
+ ret i32 %b
+}
More information about the llvm-commits
mailing list