InstCombine: Make OptimizePointerDifference more aggressive.

- Ignore pointer casts.
- Also expand GEPs that aren't constantexprs when they have one use or only constant indices.

- We now compile "&foo[i] - &foo[j]" into "i - j".

llvm-svn: 150961

1 files changed, 26 insertions, 0 deletions

diff --git a/llvm/test/Transforms/InstCombine/sub.ll b/llvm/test/Transforms/InstCombine/sub.ll
index 37de3281358..b71ec8c98f8 100644
--- a/llvm/test/Transforms/InstCombine/sub.ll
+++ b/llvm/test/Transforms/InstCombine/sub.ll
@@ -301,3 +301,29 @@ define i32 @test28(i32 %x, i32 %y, i32 %z) {
 ; CHECK-NEXT: add i32
 ; CHECK-NEXT: ret i32
 }
+
+define i64 @test29(i8* %foo, i64 %i, i64 %j) {
+  %gep1 = getelementptr inbounds i8* %foo, i64 %i
+  %gep2 = getelementptr inbounds i8* %foo, i64 %j
+  %cast1 = ptrtoint i8* %gep1 to i64
+  %cast2 = ptrtoint i8* %gep2 to i64
+  %sub = sub i64 %cast1, %cast2
+  ret i64 %sub
+; CHECK: @test29
+; CHECK-NEXT: sub i64 %i, %j
+; CHECK-NEXT: ret i64
+}
+
+define i64 @test30(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 = ptrtoint i32* %gep1 to i64
+  %cast2 = ptrtoint i8* %gep2 to i64
+  %sub = sub i64 %cast1, %cast2
+  ret i64 %sub
+; CHECK: @test30
+; CHECK-NEXT: %gep1.idx = shl nuw i64 %i, 2
+; CHECK-NEXT: sub i64 %gep1.idx, %j
+; CHECK-NEXT: ret i64
+}