InstCombine: Canonicalize (gep i8* X, -(ptrtoint Y)) to (sub (ptrtoint X), (ptrtoint Y))

The GEP pattern is what SCEV expander emits for "ugly geps". The latter is what
you get for pointer subtraction in C code. The rest of instcombine already
knows how to deal with that so just canonicalize on that.

llvm-svn: 191090

1 files changed, 14 insertions, 0 deletions

diff --git a/llvm/test/Transforms/InstCombine/getelementptr.ll b/llvm/test/Transforms/InstCombine/getelementptr.ll
index ff8ad63cef3..191a151b6b0 100644
--- a/llvm/test/Transforms/InstCombine/getelementptr.ll
+++ b/llvm/test/Transforms/InstCombine/getelementptr.ll
@@ -762,4 +762,18 @@ define i8 @test_gep_bitcast_array_different_size_element_as1([100 x double] addr
   ret i8 %x
 }
 
+define i64 @test40() {
+  %array = alloca [3 x i32], align 4
+  %gep = getelementptr inbounds [3 x i32]* %array, i64 0, i64 2
+  %gepi8 = bitcast i32* %gep to i8*
+  %p = ptrtoint [3 x i32]* %array to i64
+  %np = sub i64 0, %p
+  %gep2 = getelementptr i8* %gepi8, i64 %np
+  %ret = ptrtoint i8* %gep2 to i64
+  ret i64 %ret
+
+; CHECK-LABEL: @test40
+; CHECK-NEXT: ret i64 8
+}
+
 ; CHECK: attributes [[NUW]] = { nounwind }