Change IR generation for return (in the simple case) to avoid doing silly

load/store nonsense in the epilog.  For example, for:

int foo(int X) {
  int A[100];
  return A[X];
}

we used to generate:

  %arrayidx = getelementptr inbounds [100 x i32]* %A, i32 0, i64 %idxprom ; <i32*> [#uses=1]
  %tmp1 = load i32* %arrayidx                     ; <i32> [#uses=1]
  store i32 %tmp1, i32* %retval
  %0 = load i32* %retval                          ; <i32> [#uses=1]
  ret i32 %0
}

which codegen'd to this code:

_foo:                                   ## @foo
## BB#0:                                ## %entry
	subq	$408, %rsp              ## imm = 0x198
	movl	%edi, 400(%rsp)
	movl	400(%rsp), %edi
	movslq	%edi, %rax
	movl	(%rsp,%rax,4), %edi
	movl	%edi, 404(%rsp)
	movl	404(%rsp), %eax
	addq	$408, %rsp              ## imm = 0x198
	ret

Now we generate:

  %arrayidx = getelementptr inbounds [100 x i32]* %A, i32 0, i64 %idxprom ; <i32*> [#uses=1]
  %tmp1 = load i32* %arrayidx                     ; <i32> [#uses=1]
  ret i32 %tmp1
}

and:

_foo:                                   ## @foo
## BB#0:                                ## %entry
	subq	$408, %rsp              ## imm = 0x198
	movl	%edi, 404(%rsp)
	movl	404(%rsp), %edi
	movslq	%edi, %rax
	movl	(%rsp,%rax,4), %eax
	addq	$408, %rsp              ## imm = 0x198
	ret

This actually does matter, cutting out 2000 lines of IR from CGStmt.ll 
for example.

Another interesting effect is that altivec.h functions which are dead
now get dce'd by the inliner.  Hence all the changes to 
builtins-ppc-altivec.c to ensure the calls aren't dead.





git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@106970 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 3 insertions, 4 deletions

diff --git a/test/CodeGenCXX/references.cpp b/test/CodeGenCXX/references.cpp
index 6fc610298b..ed0c6f9d2d 100644
--- a/test/CodeGenCXX/references.cpp
+++ b/test/CodeGenCXX/references.cpp
@@ -150,10 +150,9 @@ void f0(s1 a) { s1 b = a; }
 
 // PR6024
 // CHECK: @_Z2f2v()
-// CHECK: alloca
-// CHECK: store
-// CHECK: load
-// CHECK: ret
+// CHECK: alloca i32,
+// CHECK-NEXT: store
+// CHECK-NEXT: ret
 const int &f2() { return 0; }
 
 // Don't constant fold const reference parameters with default arguments to