[InstCombine] (icmp sgt smin(PosA, B) 0) -> (icmp sgt B 0)

When checking whether an smin is positive, we can move the comparison to one of the inputs if the other is known positive. If the known positive one is the min, then the other can't be negative. If the other is the min, then we compute the min.

Differential Revision: http://reviews.llvm.org/D17873

llvm-svn: 263059

1 files changed, 13 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 6ee0525ea18..703506d8098 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3173,6 +3173,19 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
         return Res;
     }
 
+    // (icmp sgt smin(PosA, B) 0) -> (icmp sgt B 0)
+    if (CI->isZero() && I.getPredicate() == ICmpInst::ICMP_SGT)
+      if (auto *SI = dyn_cast<SelectInst>(Op0)) {
+        SelectPatternResult SPR = matchSelectPattern(SI, A, B);
+        if (SPR.Flavor == SPF_SMIN) {
+          if (isKnownNonNegative(A, DL) && isKnownNonZero(A, DL))
+            return new ICmpInst(I.getPredicate(), B, CI);
+          if (isKnownNonNegative(B, DL) && isKnownNonZero(B, DL))
+            return new ICmpInst(I.getPredicate(), A, CI);
+        }
+      }
+    
+
     // The following transforms are only 'worth it' if the only user of the
     // subtraction is the icmp.
     if (Op0->hasOneUse()) {