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Fix x86 fast-isel's cmp+branch folding to avoid folding when the

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comparison is in a different basic block from the branch. In such
cases, the comparison's operands may not have initialized virtual
registers available.

llvm-svn: 111709
This commit is contained in:
Dan Gohman 2010-08-21 02:32:36 +00:00
parent 1998fbbf1a
commit 30b8e6cfd2
2 changed files with 33 additions and 2 deletions
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6
lib/Target/X86/X86FastISel.cpp
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@ -960,9 +960,11 @@ bool X86FastISel::X86SelectBranch(const Instruction *I) {
MachineBasicBlock *TrueMBB = FuncInfo.MBBMap[BI->getSuccessor(0)];
MachineBasicBlock *FalseMBB = FuncInfo.MBBMap[BI->getSuccessor(1)];
// Fold the common case of a conditional branch with a comparison.
// Fold the common case of a conditional branch with a comparison
// in the same block (values defined on other blocks may not have
// initialized registers).
if (const CmpInst *CI = dyn_cast<CmpInst>(BI->getCondition())) {
if (CI->hasOneUse()) {
if (CI->hasOneUse() && CI->getParent() == I->getParent()) {
EVT VT = TLI.getValueType(CI->getOperand(0)->getType());
// Try to take advantage of fallthrough opportunities.

29
test/CodeGen/X86/fast-isel-cmp-branch.ll Normal file
View File

@ -0,0 +1,29 @@
; RUN: llc -O0 -march=x86-64 -asm-verbose=false < %s | FileCheck %s
; rdar://8337108
; Fast-isel shouldn't try to look through the compare because it's in a
; different basic block, so its operands aren't necessarily exported
; for cross-block usage.
; CHECK: movb %al, 7(%rsp)
; CHECK: callq {{_?}}bar
; CHECK: movb 7(%rsp), %al
declare void @bar()
define void @foo(i32 %a, i32 %b) nounwind {
entry:
%q = add i32 %a, 7
%r = add i32 %b, 9
%t = icmp ult i32 %q, %r
invoke void @bar() to label %next unwind label %unw
next:
br i1 %t, label %true, label %return
true:
call void @bar()
br label %return
return:
ret void
unw:
unreachable
}