Author: clamb
Date: Tue Dec 18 15:32:20 2007
New Revision: 45173
URL: http://llvm.org/viewvc/llvm-project?rev=45173&view=rev
Log:
Fold subtracts into integer compares vs. zero. This improves generate code for
this case on X86
from
_foo:
movl $99, %ecx
movl 4(%esp), %eax
subl %eax, %ecx
xorl %edx, %edx
testl %ecx, %ecx
cmovs %edx, %eax
ret
to
_foo:
xorl %ecx, %ecx
movl 4(%esp), %eax
cmpl $99, %eax
cmovg %ecx, %eax
ret
Modified:
llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
Modified: llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
URL:
http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp?rev=45173&r1=45172&r2=45173&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp Tue Dec 18
15:32:20 2007
@@ -4793,7 +4793,24 @@
if (isa<UndefValue>(Op1)) // X icmp undef -> undef
return ReplaceInstUsesWith(I, UndefValue::get(Type::Int1Ty));
-
+
+ // (icmp cond (sub m A) 0) ->
+ // (icmp cond m A)
+ {
+ ConstantInt *C1, *C2;
+ Value *A;
+ // Check both arguments of the compare for a matching subtract.
+ if (match(Op0, m_ConstantInt(C1)) && C1->getValue() == 0 &&
+ match(Op1, m_Sub(m_ConstantInt(C2), m_Value(A)))) {
+ // We managed to fold the add into the RHS of the select condition.
+ return new ICmpInst(I.getPredicate(), A, C2);
+ } else if (match(Op1, m_ConstantInt(C1)) && C1->getValue() == 0 &&
+ match(Op0, m_Sub(m_ConstantInt(C2), m_Value(A)))) {
+ // We managed to fold the add into the LHS of the select condition.
+ return new ICmpInst(I.getPredicate(), C2, A);
+ }
+ }
+
// icmp <global/alloca*/null>, <global/alloca*/null> - Global/Stack value
// addresses never equal each other! We already know that Op0 != Op1.
if ((isa<GlobalValue>(Op0) || isa<AllocaInst>(Op0) ||
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