[LSR] Don't try and create post-inc expressions on non-rotated loops

If a loop is not rotated (for example when optimizing for size), the latch is not the backedge. If we promote an expression to post-inc form, we not only increase register pressure and add a COPY for that IV expression but for all IVs!

Motivating testcase:

    void f(float *a, float *b, float *c, int n) {
      while (n-- > 0)
        *c++ = *a++ + *b++;
    }

It's imperative that the pointer increments be located in the latch block and not the header block; if not, we cannot use post-increment loads and stores and we have to keep both the post-inc and pre-inc values around until the end of the latch which bloats register usage.

llvm-svn: 278658

1 files changed, 2 insertions, 2 deletions

diff --git a/llvm/test/CodeGen/X86/lsr-loop-exit-cond.ll b/llvm/test/CodeGen/X86/lsr-loop-exit-cond.ll
index 2e3929be31c..240026164e6 100644
--- a/llvm/test/CodeGen/X86/lsr-loop-exit-cond.ll
+++ b/llvm/test/CodeGen/X86/lsr-loop-exit-cond.ll
@@ -3,12 +3,12 @@
 
 ; CHECK-LABEL: t:
 ; CHECK: movl (%r9,%rax,4), %e{{..}}
-; CHECK-NEXT: decq
+; CHECK-NEXT: testq
 ; CHECK-NEXT: jne
 
 ; ATOM-LABEL: t:
 ; ATOM: movl (%r9,%r{{.+}},4), %e{{..}}
-; ATOM-NEXT: decq
+; ATOM-NEXT: testq
 ; ATOM-NEXT: jne
 
 @Te0 = external global [256 x i32]		; <[256 x i32]*> [#uses=5]