[llvm-commits] [llvm] r132815 - /llvm/trunk/lib/Target/X86/README-X86-64.txt
Eli Friedman
eli.friedman at gmail.com
Thu Jun 9 16:02:19 PDT 2011
Author: efriedma
Date: Thu Jun 9 18:02:19 2011
New Revision: 132815
URL: http://llvm.org/viewvc/llvm-project?rev=132815&view=rev
Log:
Chris fixed this README a while back by changing how clang generates code for structs like the given struct.
Modified:
llvm/trunk/lib/Target/X86/README-X86-64.txt
Modified: llvm/trunk/lib/Target/X86/README-X86-64.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/README-X86-64.txt?rev=132815&r1=132814&r2=132815&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/README-X86-64.txt (original)
+++ llvm/trunk/lib/Target/X86/README-X86-64.txt Thu Jun 9 18:02:19 2011
@@ -124,51 +124,6 @@
//===---------------------------------------------------------------------===//
-Take the following C code
-(from http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43640):
-
-struct u1
-{
- float x;
- float y;
-};
-
-float foo(struct u1 u)
-{
- return u.x + u.y;
-}
-
-Optimizes to the following IR:
-define float @foo(double %u.0) nounwind readnone {
-entry:
- %tmp8 = bitcast double %u.0 to i64 ; <i64> [#uses=2]
- %tmp6 = trunc i64 %tmp8 to i32 ; <i32> [#uses=1]
- %tmp7 = bitcast i32 %tmp6 to float ; <float> [#uses=1]
- %tmp2 = lshr i64 %tmp8, 32 ; <i64> [#uses=1]
- %tmp3 = trunc i64 %tmp2 to i32 ; <i32> [#uses=1]
- %tmp4 = bitcast i32 %tmp3 to float ; <float> [#uses=1]
- %0 = fadd float %tmp7, %tmp4 ; <float> [#uses=1]
- ret float %0
-}
-
-And current llvm-gcc/clang output:
- movd %xmm0, %rax
- movd %eax, %xmm1
- shrq $32, %rax
- movd %eax, %xmm0
- addss %xmm1, %xmm0
- ret
-
-We really shouldn't move the floats to RAX, only to immediately move them
-straight back to the XMM registers.
-
-There really isn't any good way to handle this purely in IR optimizers; it
-could possibly be handled by changing the output of the fronted, though. It
-would also be feasible to add a x86-specific DAGCombine to optimize the
-bitcast+trunc+(lshr+)bitcast combination.
-
-//===---------------------------------------------------------------------===//
-
Take the following code
(from http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34653):
extern unsigned long table[];
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