[llvm-commits] [llvm] r119922 - in /llvm/trunk: lib/Target/README.txt lib/Transforms/InstCombine/InstCombineCompares.cpp test/Transforms/InstCombine/icmp.ll
Chris Lattner
sabre at nondot.org
Sat Nov 20 22:44:42 PST 2010
Author: lattner
Date: Sun Nov 21 00:44:42 2010
New Revision: 119922
URL: http://llvm.org/viewvc/llvm-project?rev=119922&view=rev
Log:
optimize:
void a(int x) { if (((1<<x)&8)==0) b(); }
into "x != 3", which occurs over 100 times in 403.gcc but in no
other program in llvm-test.
Modified:
llvm/trunk/lib/Target/README.txt
llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
llvm/trunk/test/Transforms/InstCombine/icmp.ll
Modified: llvm/trunk/lib/Target/README.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/README.txt?rev=119922&r1=119921&r2=119922&view=diff
==============================================================================
--- llvm/trunk/lib/Target/README.txt (original)
+++ llvm/trunk/lib/Target/README.txt Sun Nov 21 00:44:42 2010
@@ -1699,14 +1699,6 @@
//===---------------------------------------------------------------------===//
-Missed instcombine transformation:
-void b();
-void a(int x) { if (((1<<x)&8)==0) b(); }
-
-The shift should be optimized out. Testcase derived from gcc.
-
-//===---------------------------------------------------------------------===//
-
Missed instcombine or reassociate transformation:
int a(int a, int b) { return (a==12)&(b>47)&(b<58); }
Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=119922&r1=119921&r2=119922&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp Sun Nov 21 00:44:42 2010
@@ -1744,14 +1744,84 @@
// simplify this comparison. For example, (x&4) < 8 is always true.
switch (I.getPredicate()) {
default: llvm_unreachable("Unknown icmp opcode!");
- case ICmpInst::ICMP_EQ:
+ case ICmpInst::ICMP_EQ: {
if (Op0Max.ult(Op1Min) || Op0Min.ugt(Op1Max))
return ReplaceInstUsesWith(I, ConstantInt::getFalse(I.getContext()));
+
+ // If all bits are known zero except for one, then we know at most one
+ // bit is set. If the comparison is against zero, then this is a check
+ // to see if *that* bit is set.
+ APInt Op0KnownZeroInverted = ~Op0KnownZero;
+ if (~Op1KnownZero == 0 && Op0KnownZeroInverted.isPowerOf2()) {
+ // If the LHS is an AND with the same constant, look through it.
+ Value *LHS = 0;
+ ConstantInt *LHSC = 0;
+ if (!match(Op0, m_And(m_Value(LHS), m_ConstantInt(LHSC))) ||
+ LHSC->getValue() != Op0KnownZeroInverted)
+ LHS = Op0;
+
+ // If the LHS is 1 << x, and we know the result is a power of 2 like 8,
+ // then turn "((1 << x)&8) == 0" into "x == 3".
+ Value *X = 0;
+ if (match(LHS, m_Shl(m_One(), m_Value(X)))) {
+ unsigned CmpVal = Op0KnownZeroInverted.countTrailingZeros();
+ return new ICmpInst(ICmpInst::ICMP_EQ, X,
+ ConstantInt::get(X->getType(), CmpVal));
+ }
+
+ // If the LHS is 8 >>u x, and we know the result is a power of 2 like 1,
+ // then turn "((8 >>u x)&1) == 0" into "x == 3".
+ ConstantInt *CI = 0;
+ if (Op0KnownZeroInverted == 1 &&
+ match(LHS, m_LShr(m_ConstantInt(CI), m_Value(X))) &&
+ CI->getValue().isPowerOf2()) {
+ unsigned CmpVal = CI->getValue().countTrailingZeros();
+ return new ICmpInst(ICmpInst::ICMP_EQ, X,
+ ConstantInt::get(X->getType(), CmpVal));
+ }
+ }
+
break;
- case ICmpInst::ICMP_NE:
+ }
+ case ICmpInst::ICMP_NE: {
if (Op0Max.ult(Op1Min) || Op0Min.ugt(Op1Max))
return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext()));
+
+ // If all bits are known zero except for one, then we know at most one
+ // bit is set. If the comparison is against zero, then this is a check
+ // to see if *that* bit is set.
+ APInt Op0KnownZeroInverted = ~Op0KnownZero;
+ if (~Op1KnownZero == 0 && Op0KnownZeroInverted.isPowerOf2()) {
+ // If the LHS is an AND with the same constant, look through it.
+ Value *LHS = 0;
+ ConstantInt *LHSC = 0;
+ if (!match(Op0, m_And(m_Value(LHS), m_ConstantInt(LHSC))) ||
+ LHSC->getValue() != Op0KnownZeroInverted)
+ LHS = Op0;
+
+ // If the LHS is 1 << x, and we know the result is a power of 2 like 8,
+ // then turn "((1 << x)&8) != 0" into "x != 3".
+ Value *X = 0;
+ if (match(LHS, m_Shl(m_One(), m_Value(X)))) {
+ unsigned CmpVal = Op0KnownZeroInverted.countTrailingZeros();
+ return new ICmpInst(ICmpInst::ICMP_NE, X,
+ ConstantInt::get(X->getType(), CmpVal));
+ }
+
+ // If the LHS is 8 >>u x, and we know the result is a power of 2 like 1,
+ // then turn "((8 >>u x)&1) != 0" into "x != 3".
+ ConstantInt *CI = 0;
+ if (Op0KnownZeroInverted == 1 &&
+ match(LHS, m_LShr(m_ConstantInt(CI), m_Value(X))) &&
+ CI->getValue().isPowerOf2()) {
+ unsigned CmpVal = CI->getValue().countTrailingZeros();
+ return new ICmpInst(ICmpInst::ICMP_NE, X,
+ ConstantInt::get(X->getType(), CmpVal));
+ }
+ }
+
break;
+ }
case ICmpInst::ICMP_ULT:
if (Op0Max.ult(Op1Min)) // A <u B -> true if max(A) < min(B)
return ReplaceInstUsesWith(I, ConstantInt::getTrue(I.getContext()));
Modified: llvm/trunk/test/Transforms/InstCombine/icmp.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/icmp.ll?rev=119922&r1=119921&r2=119922&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/icmp.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/icmp.ll Sun Nov 21 00:44:42 2010
@@ -154,3 +154,41 @@
; CHECK: @test16
; CHECK: ret i1 undef
}
+
+define i1 @test17(i32 %x) nounwind {
+ %shl = shl i32 1, %x
+ %and = and i32 %shl, 8
+ %cmp = icmp eq i32 %and, 0
+ ret i1 %cmp
+; CHECK: @test17
+; CHECK-NEXT: %cmp = icmp eq i32 %x, 3
+}
+
+
+define i1 @test18(i32 %x) nounwind {
+ %sh = lshr i32 8, %x
+ %and = and i32 %sh, 1
+ %cmp = icmp eq i32 %and, 0
+ ret i1 %cmp
+; CHECK: @test18
+; CHECK-NEXT: %cmp = icmp eq i32 %x, 3
+}
+
+define i1 @test19(i32 %x) nounwind {
+ %shl = shl i32 1, %x
+ %and = and i32 %shl, 8
+ %cmp = icmp eq i32 %and, 8
+ ret i1 %cmp
+; CHECK: @test19
+; CHECK-NEXT: %cmp = icmp ne i32 %x, 3
+}
+
+define i1 @test20(i32 %x) nounwind {
+ %shl = shl i32 1, %x
+ %and = and i32 %shl, 8
+ %cmp = icmp ne i32 %and, 0
+ ret i1 %cmp
+; CHECK: @test20
+; CHECK-NEXT: %cmp = icmp ne i32 %x, 3
+}
+
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