Eliminate a bitwise 'not' op of 'not' min/max by inverting the min/max.
Bitwise 'not' of the min/max could be eliminated in the pattern:
%notx = xor i32 %x, -1
%cmp1 = icmp sgt[slt/ugt/ult] i32 %notx, %y
%smax = select i1 %cmp1, i32 %notx, i32 %y
%res = xor i32 %smax, -1
https://rise4fun.com/Alive/lCN
Reviewers: spatel
Reviewed by: spatel
Subscribers: a.elovikov, llvm-commits
Differential Revision: https://reviews.llvm.org/D45317
llvm-svn: 329791
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 04a85c7..9ba92f7 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2696,5 +2696,35 @@
return SelectInst::Create(Cmp, Builder.CreateNeg(A), A);
}
+ // Eliminate a bitwise 'not' op of 'not' min/max by inverting the min/max:
+ //
+ // %notx = xor i32 %x, -1
+ // %cmp1 = icmp sgt i32 %notx, %y
+ // %smax = select i1 %cmp1, i32 %notx, i32 %y
+ // %res = xor i32 %smax, -1
+ // =>
+ // %noty = xor i32 %y, -1
+ // %cmp2 = icmp slt %x, %noty
+ // %res = select i1 %cmp2, i32 %x, i32 %noty
+ //
+ // Same is applicable for smin/umax/umin.
+ {
+ Value *LHS, *RHS;
+ SelectPatternFlavor SPF = matchSelectPattern(Op0, LHS, RHS).Flavor;
+ if (Op0->hasOneUse() && SelectPatternResult::isMinOrMax(SPF) &&
+ match(Op1, m_AllOnes())) {
+
+ Value *X;
+ if (match(RHS, m_Not(m_Value(X))))
+ std::swap(RHS, LHS);
+
+ if (match(LHS, m_Not(m_Value(X)))) {
+ Value *NotY = Builder.CreateNot(RHS);
+ return SelectInst::Create(
+ Builder.CreateICmp(getInverseMinMaxPred(SPF), X, NotY), X, NotY);
+ }
+ }
+ }
+
return Changed ? &I : nullptr;
}