Implement rdar://7530813 - collapse multiple GEP instructions in IRgen

This avoids generating two gep's for common array operations.  Before
we would generate something like:

  %tmp = load i32* %X.addr                        ; <i32> [#uses=1]
  %arraydecay = getelementptr inbounds [100 x i32]* %A, i32 0, i32 0 ; <i32*> [#uses=1]
  %arrayidx = getelementptr inbounds i32* %arraydecay, i32 %tmp ; <i32*> [#uses=1]
  %tmp1 = load i32* %arrayidx                     ; <i32> [#uses=1]

Now we generate:

  %tmp = load i32* %X.addr                        ; <i32> [#uses=1]
  %arrayidx = getelementptr inbounds [100 x i32]* %A, i32 0, i32 %tmp ; <i32*> [#uses=1]
  %tmp1 = load i32* %arrayidx                     ; <i32> [#uses=1]

Less IR is better at -O0.

llvm-svn: 106966

1 files changed, 13 insertions, 1 deletions

diff --git a/clang/test/CodeGen/exprs.c b/clang/test/CodeGen/exprs.c
index d182ce81cab..010e6e3cf51 100644
--- a/clang/test/CodeGen/exprs.c
+++ b/clang/test/CodeGen/exprs.c
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 %s -emit-llvm -o - 
+// RUN: %clang_cc1 %s -emit-llvm -o - | FileCheck %s
 
 // PR1895
 // sizeof function
@@ -119,3 +119,15 @@ void f9(struct S *x) {
 void f10() {
   __builtin_sin(0);
 }
+
+// rdar://7530813
+// CHECK: define i32 @f11
+int f11(long X) {
+  int A[100];
+  return A[X];
+
+// CHECK: load {{.*}}* %X.addr
+// CHECK-NEXT: getelementptr inbounds [100 x i32]* %A, i32 0, 
+// CHECK-NEXT: load i32*
+}
+