From e7cf062537e898f830565db5dbf99ae9c928399e Mon Sep 17 00:00:00 2001 From: Benjamin Kramer Date: Fri, 22 Apr 2011 18:47:44 +0000 Subject: DAGCombine: fold "(zext x) == C" into "x == (trunc C)" if the trunc is lossless. On x86 this allows to fold a load into the cmp, greatly reducing register pressure. movzbl (%rdi), %eax cmpl $47, %eax -> cmpb $47, (%rdi) This shaves 8k off gcc.o on i386. I'll leave applying the patch in README.txt to Chris :) git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@130005 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Target/README.txt | 31 +------------------------------ 1 file changed, 1 insertion(+), 30 deletions(-) (limited to 'lib/Target') diff --git a/lib/Target/README.txt b/lib/Target/README.txt index 5032b2bbbb..c345ce50c0 100644 --- a/lib/Target/README.txt +++ b/lib/Target/README.txt @@ -2259,34 +2259,6 @@ icmp transform. //===---------------------------------------------------------------------===// -These functions: -int foo(int *X) { - if ((*X & 255) == 47) - bar(); -} -int foo2(int X) { - if ((X & 255) == 47) - bar(); -} - -codegen to: - - movzbl (%rdi), %eax - cmpl $47, %eax - jne LBB0_2 - -and: - movzbl %dil, %eax - cmpl $47, %eax - jne LBB1_2 - -If a dag combine shrunk the compare to a byte compare, then we'd fold the load -in the first example, and eliminate the movzbl in the second, saving a register. -This can be a target independent dag combine that works on ISD::SETCC, it would -catch this before the legalize ops pass. - -//===---------------------------------------------------------------------===// - We should optimize this: %tmp = load i16* %arrayidx, align 4, !tbaa !0 @@ -2329,8 +2301,7 @@ Index: InstCombine/InstCombineCompares.cpp { -but we can't do that until the dag combine above is added. Not having this -is blocking resolving PR6627. +Not having this is blocking resolving PR6627. //===---------------------------------------------------------------------===// -- cgit v1.2.3