if (BinaryOperator::isNeg(Sub) || BinaryOperator::isFNeg(Sub))
return false;
+ // Don't breakup X - undef.
+ if (isa<UndefValue>(Sub->getOperand(1)))
+ return false;
+
// Don't bother to break this up unless either the LHS is an associable add or
// subtract or if this is only used by one.
Value *V0 = Sub->getOperand(0);
--- /dev/null
+; RUN: opt -reassociate -S < %s | FileCheck %s
+; PR21205
+
+@a = common global i32 0, align 4
+@b = common global i32 0, align 4
+
+; Don't canonicalize %conv - undef into %conv + (-undef).
+; CHECK-LABEL: @test1
+; CHECK: %sub = fsub fast float %conv, undef
+; CHECK: %sub1 = fadd fast float %sub, -1.000000e+00
+
+define i32 @test1() {
+entry:
+ %0 = load i32* @a, align 4
+ %conv = sitofp i32 %0 to float
+ %sub = fsub fast float %conv, undef
+ %sub1 = fadd fast float %sub, -1.000000e+00
+ %conv2 = fptosi float %sub1 to i32
+ store i32 %conv2, i32* @b, align 4
+ ret i32 undef
+}