From b62e24784c81605fa82143db6f8f97310bc6ca98 Mon Sep 17 00:00:00 2001
From: Quentin Colombet <qcolombet@apple.com>
Date: Tue, 26 Apr 2016 23:14:24 +0000
Subject: [PATCH] [MachineInstrBundle] Improvement the recognition of dead
 definitions.

Now, it is possible to know that partial definitions are dead definitions and
recognize that clobbered registers are also dead.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@267621 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/CodeGen/MachineInstrBundle.h |  4 ++++
 lib/CodeGen/MachineInstrBundle.cpp        | 10 +++++++---
 test/CodeGen/X86/cmpxchg-clobber-flags.ll |  3 +--
 3 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/include/llvm/CodeGen/MachineInstrBundle.h b/include/llvm/CodeGen/MachineInstrBundle.h
index 9b374cf7991..fd828d4959d 100644
--- a/include/llvm/CodeGen/MachineInstrBundle.h
+++ b/include/llvm/CodeGen/MachineInstrBundle.h
@@ -187,6 +187,10 @@ public:
     /// dead.
     bool DeadDef;
 
+    /// Reg is Defined and all defs of reg or an overlapping register are
+    /// dead.
+    bool PartialDeadDef;
+
     /// There is a use operand of reg or a super-register with kill flag set.
     bool Killed;
   };
diff --git a/lib/CodeGen/MachineInstrBundle.cpp b/lib/CodeGen/MachineInstrBundle.cpp
index 4619daf3014..725237b5644 100644
--- a/lib/CodeGen/MachineInstrBundle.cpp
+++ b/lib/CodeGen/MachineInstrBundle.cpp
@@ -293,7 +293,7 @@ MachineOperandIteratorBase::PhysRegInfo
 MachineOperandIteratorBase::analyzePhysReg(unsigned Reg,
                                            const TargetRegisterInfo *TRI) {
   bool AllDefsDead = true;
-  PhysRegInfo PRI = {false, false, false, false, false, false, false};
+  PhysRegInfo PRI = {false, false, false, false, false, false, false, false};
 
   assert(TargetRegisterInfo::isPhysicalRegister(Reg) &&
          "analyzePhysReg not given a physical register!");
@@ -332,8 +332,12 @@ MachineOperandIteratorBase::analyzePhysReg(unsigned Reg,
     }
   }
 
-  if (AllDefsDead && PRI.FullyDefined)
-    PRI.DeadDef = true;
+  if (AllDefsDead) {
+    if (PRI.FullyDefined || PRI.Clobbered)
+      PRI.DeadDef = true;
+    else
+      PRI.PartialDeadDef = true;
+  }
 
   return PRI;
 }
diff --git a/test/CodeGen/X86/cmpxchg-clobber-flags.ll b/test/CodeGen/X86/cmpxchg-clobber-flags.ll
index 6f54a0435f8..74599cbdc17 100644
--- a/test/CodeGen/X86/cmpxchg-clobber-flags.ll
+++ b/test/CodeGen/X86/cmpxchg-clobber-flags.ll
@@ -63,11 +63,10 @@ define i64 @test_intervening_call(i64* %foo, i64 %bar, i64 %baz) {
 ; x8664-sahf-NEXT: popq %rax
 ; x8664-sahf-NEXT: movq %rax, %rdi
 ; x8664-sahf-NEXT: callq bar
-; x8664-sahf-NEXT: pushq %rax
+; RAX is dead, no need to push and pop it.
 ; x8664-sahf-NEXT: movq [[FLAGS]], %rax
 ; x8664-sahf-NEXT: addb $127, %al
 ; x8664-sahf-NEXT: sahf
-; x8664-sahf-NEXT: popq %rax
 ; x8664-sahf-NEXT: jne
 
   %cx = cmpxchg i64* %foo, i64 %bar, i64 %baz seq_cst seq_cst