X86InstrInfo::copyPhysReg: workaround reg liveness

Summary:
computeRegisterLiveness and analyzePhysReg are currently getting
confused about liveness in some cases, breaking copyPhysReg's
calculation of whether AX is dead in some cases. Work around this issue
temporarily by assuming that AX is always live.

See detail in: https://llvm.org/bugs/show_bug.cgi?id=25033#c7
And associated bugs PR24535 PR25033 PR24991 PR24992 PR25201.

This workaround makes the code correct but slightly inefficient, but it
seems to confuse the machine instr verifier which now things EAX was
undefined in some cases where it's being conservatively saved /
restored.

Reviewers: majnemer, sanjoy
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D15198

llvm-svn: 254680

1 files changed, 39 insertions, 4 deletions

diff --git a/llvm/test/CodeGen/X86/cmpxchg-clobber-flags.ll b/llvm/test/CodeGen/X86/cmpxchg-clobber-flags.ll
index c129128b5fa..791edba89c4 100644
--- a/llvm/test/CodeGen/X86/cmpxchg-clobber-flags.ll
+++ b/llvm/test/CodeGen/X86/cmpxchg-clobber-flags.ll
@@ -1,7 +1,14 @@
-; RUN: llc -verify-machineinstrs -mtriple=i386-linux-gnu %s -o - | FileCheck %s -check-prefix=i386
-; RUN: llc -verify-machineinstrs -mtriple=i386-linux-gnu -pre-RA-sched=fast %s -o - | FileCheck %s -check-prefix=i386f
-; RUN: llc -verify-machineinstrs -mtriple=x86_64-linux-gnu %s -o - | FileCheck %s -check-prefix=x8664
-; RUN: llc -verify-machineinstrs -mtriple=x86_64-linux-gnu -pre-RA-sched=fast %s -o - | FileCheck %s -check-prefix=x8664
+; RUN: llc -mtriple=i386-linux-gnu %s -o - | FileCheck %s -check-prefix=i386
+; RUN: llc -mtriple=i386-linux-gnu -pre-RA-sched=fast %s -o - | FileCheck %s -check-prefix=i386f
+; RUN: llc -mtriple=x86_64-linux-gnu %s -o - | FileCheck %s -check-prefix=x8664
+; RUN: llc -mtriple=x86_64-linux-gnu -pre-RA-sched=fast %s -o - | FileCheck %s -check-prefix=x8664
+
+; FIXME: X86InstrInfo::copyPhysReg had code which figured out whether AX was
+;        live or not to avoid save / restore when it's not needed. See FIXME in
+;        that function for more details on which the code is currently
+;        disabled. The extra push/pop are marked below and can be removed once
+;        the issue is fixed.
+;        -verify-machineinstrs should also be added back in the RUN lines above.
 
 declare i32 @foo()
 declare i32 @bar(i64)
@@ -17,22 +24,34 @@ define i64 @test_intervening_call(i64* %foo, i64 %bar, i64 %baz) {
 ; i386-NEXT: movl %edx, 4(%esp)
 ; i386-NEXT: movl %eax, (%esp)
 ; i386-NEXT: calll bar
+; ** FIXME Next line isn't actually necessary. **
+; i386-NEXT: pushl %eax
 ; i386-NEXT: movl [[FLAGS]], %eax
 ; i386-NEXT: addb $127, %al
 ; i386-NEXT: sahf
+; ** FIXME Next line isn't actually necessary. **
+; i386-NEXT: popl %eax
 ; i386-NEXT: jne
 
 ; i386f-LABEL: test_intervening_call:
 ; i386f: cmpxchg8b
 ; i386f-NEXT: movl %eax, (%esp)
 ; i386f-NEXT: movl %edx, 4(%esp)
+; ** FIXME Next line isn't actually necessary. **
+; i386f-NEXT: pushl %eax
 ; i386f-NEXT: seto %al
 ; i386f-NEXT: lahf
 ; i386f-NEXT: movl %eax, [[FLAGS:%.*]]
+; ** FIXME Next line isn't actually necessary. **
+; i386f-NEXT: popl %eax
 ; i386f-NEXT: calll bar
+; ** FIXME Next line isn't actually necessary. **
+; i386f-NEXT: pushl %eax
 ; i386f-NEXT: movl [[FLAGS]], %eax
 ; i386f-NEXT: addb $127, %al
 ; i386f-NEXT: sahf
+; ** FIXME Next line isn't actually necessary. **
+; i386f-NEXT: popl %eax
 ; i386f-NEXT: jne
 
 ; x8664-LABEL: test_intervening_call:
@@ -44,9 +63,13 @@ define i64 @test_intervening_call(i64* %foo, i64 %bar, i64 %baz) {
 ; x8664-NEXT: popq %rax
 ; x8664-NEXT: movq %rax, %rdi
 ; x8664-NEXT: callq bar
+; ** FIXME Next line isn't actually necessary. **
+; x8664-NEXT: pushq %rax
 ; x8664-NEXT: movq [[FLAGS]], %rax
 ; x8664-NEXT: addb $127, %al
 ; x8664-NEXT: sahf
+; ** FIXME Next line isn't actually necessary. **
+; x8664-NEXT: popq %rax
 ; x8664-NEXT: jne
 
   %cx = cmpxchg i64* %foo, i64 %bar, i64 %baz seq_cst seq_cst
@@ -111,9 +134,13 @@ cond.end:
 define i32 @test_feed_cmov(i32* %addr, i32 %desired, i32 %new) {
 ; i386-LABEL: test_feed_cmov:
 ; i386: cmpxchgl
+; ** FIXME Next line isn't actually necessary. **
+; i386-NEXT: pushl %eax
 ; i386-NEXT: seto %al
 ; i386-NEXT: lahf
 ; i386-NEXT: movl %eax, [[FLAGS:%.*]]
+; ** FIXME Next line isn't actually necessary. **
+; i386-NEXT: popl %eax
 ; i386-NEXT: calll foo
 ; i386-NEXT: pushl %eax
 ; i386-NEXT: movl [[FLAGS]], %eax
@@ -123,9 +150,13 @@ define i32 @test_feed_cmov(i32* %addr, i32 %desired, i32 %new) {
 
 ; i386f-LABEL: test_feed_cmov:
 ; i386f: cmpxchgl
+; ** FIXME Next line isn't actually necessary. **
+; i386f-NEXT: pushl %eax
 ; i386f-NEXT: seto %al
 ; i386f-NEXT: lahf
 ; i386f-NEXT: movl %eax, [[FLAGS:%.*]]
+; ** FIXME Next line isn't actually necessary. **
+; i386f-NEXT: popl %eax
 ; i386f-NEXT: calll foo
 ; i386f-NEXT: pushl %eax
 ; i386f-NEXT: movl [[FLAGS]], %eax
@@ -135,9 +166,13 @@ define i32 @test_feed_cmov(i32* %addr, i32 %desired, i32 %new) {
 
 ; x8664-LABEL: test_feed_cmov:
 ; x8664: cmpxchgl
+; ** FIXME Next line isn't actually necessary. **
+; x8664: pushq %rax
 ; x8664: seto %al
 ; x8664-NEXT: lahf
 ; x8664-NEXT: movq %rax, [[FLAGS:%.*]]
+; ** FIXME Next line isn't actually necessary. **
+; x8664-NEXT: popq %rax
 ; x8664-NEXT: callq foo
 ; x8664-NEXT: pushq %rax
 ; x8664-NEXT: movq [[FLAGS]], %rax