[llvm] r267622 - [MachineBasicBlock] Take advantage of the partially dead information.

[Quentin Colombet via llvm-commits]

Author: qcolombet
Date: Tue Apr 26 18:14:29 2016
New Revision: 267622

URL: http://llvm.org/viewvc/llvm-project?rev=267622&view=rev
Log:
[MachineBasicBlock] Take advantage of the partially dead information.

Thanks to that information we wouldn't lie on a register being live whereas it
is not.

Modified:
    llvm/trunk/lib/CodeGen/MachineBasicBlock.cpp
    llvm/trunk/test/CodeGen/X86/cmpxchg-clobber-flags.ll

Modified: llvm/trunk/lib/CodeGen/MachineBasicBlock.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/MachineBasicBlock.cpp?rev=267622&r1=267621&r2=267622&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/MachineBasicBlock.cpp (original)
+++ llvm/trunk/lib/CodeGen/MachineBasicBlock.cpp Tue Apr 26 18:14:29 2016
@@ -1208,8 +1208,15 @@ MachineBasicBlock::computeRegisterLivene
       if (Info.DeadDef)
         return LQR_Dead;
       // Register is (at least partially) live after a def.
-      if (Info.Defined)
-        return LQR_Live;
+      if (Info.Defined) {
+        if (!Info.PartialDeadDef)
+          return LQR_Live;
+        // As soon as we saw a partial definition (dead or not),
+        // we cannot tell if the value is partial live without
+        // tracking the lanemasks. We are not going to do this,
+        // so fall back on the remaining of the analysis.
+        break;
+      }
       // Register is dead after a full kill or clobber and no def.
       if (Info.Killed || Info.Clobbered)
         return LQR_Dead;

Modified: llvm/trunk/test/CodeGen/X86/cmpxchg-clobber-flags.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/cmpxchg-clobber-flags.ll?rev=267622&r1=267621&r2=267622&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/cmpxchg-clobber-flags.ll (original)
+++ llvm/trunk/test/CodeGen/X86/cmpxchg-clobber-flags.ll Tue Apr 26 18:14:29 2016
@@ -167,11 +167,10 @@ define i32 @test_feed_cmov(i32* %addr, i
 
 ; x8664-sahf-LABEL: test_feed_cmov:
 ; x8664-sahf: cmpxchgl
-; x8664-sahf: pushq %rax
+; RAX is dead, do not push or pop it.
 ; x8664-sahf-NEXT: seto %al
 ; x8664-sahf-NEXT: lahf
 ; x8664-sahf-NEXT: movq %rax, [[FLAGS:%.*]]
-; x8664-sahf-NEXT: popq %rax
 ; x8664-sahf-NEXT: callq foo
 ; x8664-sahf-NEXT: pushq %rax
 ; x8664-sahf-NEXT: movq [[FLAGS]], %rax