InstCombine: When comparing two GEPs that were derived from the same base pointer...

This came up in SmallVector code.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@150962 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index bb7763ddeb6a8e4f1c39613e76d8067fcd471928..5a91c7b97021c2bf100b69a0613253cdb3b2fcf5 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -607,6 +607,20 @@ Instruction *InstCombiner::FoldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
         return new ICmpInst(ICmpInst::getSignedPredicate(Cond),
                             GEPLHS->getOperand(0), GEPRHS->getOperand(0));
 
+      // If we're comparing GEPs with two base pointers that only differ in type
+      // and both GEPs have only constant indices or just one use, then fold
+      // the compare with the adjusted indices.
+      if (TD &&
+          (GEPLHS->hasAllConstantIndices() || GEPLHS->hasOneUse()) &&
+          (GEPRHS->hasAllConstantIndices() || GEPRHS->hasOneUse()) &&
+          PtrBase->stripPointerCasts() ==
+            GEPRHS->getOperand(0)->stripPointerCasts()) {
+        Value *Cmp = Builder->CreateICmp(ICmpInst::getSignedPredicate(Cond),
+                                         EmitGEPOffset(GEPLHS),
+                                         EmitGEPOffset(GEPRHS));
+        return ReplaceInstUsesWith(I, Cmp);
+      }
+
       // Otherwise, the base pointers are different and the indices are
       // different, bail out.
       return 0;

diff --git a/test/Transforms/InstCombine/icmp.ll b/test/Transforms/InstCombine/icmp.ll
index 1652e71401763e8fe50311cf66eed3687f228a7c..09152f0986787721b4a71f9344deeda9426e8308 100644 (file)
--- a/test/Transforms/InstCombine/icmp.ll
+++ b/test/Transforms/InstCombine/icmp.ll
@@ -589,3 +589,29 @@ define void @test58() nounwind {
   ret void
 }
 declare i32 @test58_d(i64)
+
+define i1 @test59(i8* %foo) {
+  %bit = bitcast i8* %foo to i32*
+  %gep1 = getelementptr inbounds i32* %bit, i64 2
+  %gep2 = getelementptr inbounds i8* %foo, i64 10
+  %cast1 = bitcast i32* %gep1 to i8*
+  %cmp = icmp ult i8* %cast1, %gep2
+  %use = ptrtoint i8* %cast1 to i64
+  %call = call i32 @test58_d(i64 %use) nounwind
+  ret i1 %cmp
+; CHECK: @test59
+; CHECK: ret i1 true
+}
+
+define i1 @test60(i8* %foo, i64 %i, i64 %j) {
+  %bit = bitcast i8* %foo to i32*
+  %gep1 = getelementptr inbounds i32* %bit, i64 %i
+  %gep2 = getelementptr inbounds i8* %foo, i64 %j
+  %cast1 = bitcast i32* %gep1 to i8*
+  %cmp = icmp ult i8* %cast1, %gep2
+  ret i1 %cmp
+; CHECK: @test60
+; CHECK-NEXT: %gep1.idx = shl nuw i64 %i, 2
+; CHECK-NEXT: icmp slt i64 %gep1.idx, %j
+; CHECK-NEXT: ret i1
+}