[PATCH] D17873: [InstCombine] (icmp sgt smin(PosA, B) 0) -> (icmp sgt B 0)

[Philip Reames via llvm-commits]

reames updated this revision to Diff 49846.
reames added a comment.

Updated patch which fixed bug Sanjoy pointed out


http://reviews.llvm.org/D17873

Files:
  lib/Transforms/InstCombine/InstCombineCompares.cpp
  test/Transforms/InstCombine/min-positive.ll

Index: test/Transforms/InstCombine/min-positive.ll
===================================================================
--- test/Transforms/InstCombine/min-positive.ll
+++ test/Transforms/InstCombine/min-positive.ll
@@ -0,0 +1,34 @@
+; RUN: opt -S -instcombine < %s | FileCheck %s
+
+ at g = external global i32
+
+define i1 @test(i32 %other) {
+; CHECK-LABEL: @test
+; CHECK: %test = icmp sgt i32 %other, 0
+  %positive = load i32, i32* @g, !range !{i32 1, i32 2048}
+  %cmp = icmp slt i32 %positive, %other
+  %sel = select i1 %cmp, i32 %positive, i32 %other
+  %test = icmp sgt i32 %sel, 0
+  ret i1 %test
+}
+
+define i1 @test2(i32 %other) {
+; CHECK-LABEL: @test2
+; CHECK: %test = icmp sgt i32 %other, 0
+  %positive = load i32, i32* @g, !range !{i32 1, i32 2048}
+  %cmp = icmp slt i32 %other, %positive
+  %sel = select i1 %cmp, i32 %other, i32 %positive
+  %test = icmp sgt i32 %sel, 0
+  ret i1 %test
+}
+
+; %positive might be zero
+define i1 @test3(i32 %other) {
+; CHECK-LABEL: @test3
+; CHECK: %test = icmp sgt i32 %sel, 0
+  %positive = load i32, i32* @g, !range !{i32 0, i32 2048}
+  %cmp = icmp slt i32 %positive, %other
+  %sel = select i1 %cmp, i32 %positive, i32 %other
+  %test = icmp sgt i32 %sel, 0
+  ret i1 %test
+}
Index: lib/Transforms/InstCombine/InstCombineCompares.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3173,6 +3173,19 @@
         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()) {


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