[llvm-commits] [llvm] r137777 - in /llvm/trunk: lib/Transforms/Scalar/SCCP.cpp test/Transforms/SCCP/undef-resolve.ll
Eli Friedman
eli.friedman at gmail.com
Tue Aug 16 15:06:31 PDT 2011
Author: efriedma
Date: Tue Aug 16 17:06:31 2011
New Revision: 137777
URL: http://llvm.org/viewvc/llvm-project?rev=137777&view=rev
Log:
A bunch of misc fixes to SCCPSolver::ResolvedUndefsIn, including a fix to stop
making random bad assumptions about instructions which are not explicitly listed.
Includes fix for rdar://9956541, a version of "undef ^ undef should return
0 because it's easier than arguing with users".
Modified:
llvm/trunk/lib/Transforms/Scalar/SCCP.cpp
llvm/trunk/test/Transforms/SCCP/undef-resolve.ll
Modified: llvm/trunk/lib/Transforms/Scalar/SCCP.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/SCCP.cpp?rev=137777&r1=137776&r2=137777&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/SCCP.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/SCCP.cpp Tue Aug 16 17:06:31 2011
@@ -1445,54 +1445,78 @@
}
continue;
}
-
+
LatticeVal &LV = getValueState(I);
if (!LV.isUndefined()) continue;
- // No instructions using structs need disambiguation.
- if (I->getOperand(0)->getType()->isStructTy())
- continue;
-
- // Get the lattice values of the first two operands for use below.
LatticeVal Op0LV = getValueState(I->getOperand(0));
LatticeVal Op1LV;
- if (I->getNumOperands() == 2) {
- // No instructions using structs need disambiguation.
- if (I->getOperand(1)->getType()->isStructTy())
- continue;
-
- // If this is a two-operand instruction, and if both operands are
- // undefs, the result stays undef.
+ if (I->getNumOperands() == 2)
Op1LV = getValueState(I->getOperand(1));
- if (Op0LV.isUndefined() && Op1LV.isUndefined())
- continue;
- }
-
// If this is an instructions whose result is defined even if the input is
// not fully defined, propagate the information.
Type *ITy = I->getType();
switch (I->getOpcode()) {
- default: break; // Leave the instruction as an undef.
+ case Instruction::ExtractValue:
+ break; // Extract of undef -> undef
+ case Instruction::Add:
+ case Instruction::Sub:
+ case Instruction::Trunc:
+ case Instruction::FPTrunc:
+ case Instruction::BitCast:
+ break; // Any undef -> undef
+ case Instruction::FSub:
+ case Instruction::FAdd:
+ case Instruction::FMul:
+ case Instruction::FDiv:
+ case Instruction::FRem:
+ // Floating-point binary operation: be conservative.
+ if (Op0LV.isUndefined() && Op1LV.isUndefined())
+ markForcedConstant(I, Constant::getNullValue(ITy));
+ else
+ markOverdefined(I);
+ return true;
case Instruction::ZExt:
- // After a zero extend, we know the top part is zero. SExt doesn't have
- // to be handled here, because we don't know whether the top part is 1's
- // or 0's.
- case Instruction::SIToFP: // some FP values are not possible, just use 0.
- case Instruction::UIToFP: // some FP values are not possible, just use 0.
+ case Instruction::SExt:
+ case Instruction::FPToUI:
+ case Instruction::FPToSI:
+ case Instruction::FPExt:
+ case Instruction::PtrToInt:
+ case Instruction::IntToPtr:
+ case Instruction::SIToFP:
+ case Instruction::UIToFP:
+ // undef -> 0; some outputs are impossible
markForcedConstant(I, Constant::getNullValue(ITy));
return true;
case Instruction::Mul:
case Instruction::And:
+ // Both operands undef -> undef
+ if (Op0LV.isUndefined() && Op1LV.isUndefined())
+ break;
// undef * X -> 0. X could be zero.
// undef & X -> 0. X could be zero.
markForcedConstant(I, Constant::getNullValue(ITy));
return true;
case Instruction::Or:
+ // Both operands undef -> undef
+ if (Op0LV.isUndefined() && Op1LV.isUndefined())
+ break;
// undef | X -> -1. X could be -1.
markForcedConstant(I, Constant::getAllOnesValue(ITy));
return true;
+ case Instruction::Xor:
+ // undef ^ undef -> 0; strictly speaking, this is not strictly
+ // necessary, but we try to be nice to people who expect this
+ // behavior in simple cases
+ if (Op0LV.isUndefined() && Op1LV.isUndefined()) {
+ markForcedConstant(I, Constant::getNullValue(ITy));
+ return true;
+ }
+ // undef ^ X -> undef
+ break;
+
case Instruction::SDiv:
case Instruction::UDiv:
case Instruction::SRem:
@@ -1507,26 +1531,24 @@
return true;
case Instruction::AShr:
- // undef >>s X -> undef. No change.
- if (Op0LV.isUndefined()) break;
-
- // X >>s undef -> X. X could be 0, X could have the high-bit known set.
- if (Op0LV.isConstant())
- markForcedConstant(I, Op0LV.getConstant());
- else
- markOverdefined(I);
+ // X >>a undef -> undef.
+ if (Op1LV.isUndefined()) break;
+
+ // undef >>a X -> all ones
+ markForcedConstant(I, Constant::getAllOnesValue(ITy));
return true;
case Instruction::LShr:
case Instruction::Shl:
- // undef >> X -> undef. No change.
- // undef << X -> undef. No change.
- if (Op0LV.isUndefined()) break;
-
- // X >> undef -> 0. X could be 0.
- // X << undef -> 0. X could be 0.
+ // X << undef -> undef.
+ // X >> undef -> undef.
+ if (Op1LV.isUndefined()) break;
+
+ // undef << X -> 0
+ // undef >> X -> 0
markForcedConstant(I, Constant::getNullValue(ITy));
return true;
case Instruction::Select:
+ Op1LV = getValueState(I->getOperand(1));
// undef ? X : Y -> X or Y. There could be commonality between X/Y.
if (Op0LV.isUndefined()) {
if (!Op1LV.isConstant()) // Pick the constant one if there is any.
@@ -1546,9 +1568,19 @@
else
markOverdefined(I);
return true;
- case Instruction::Call:
- // If a call has an undef result, it is because it is constant foldable
- // but one of the inputs was undef. Just force the result to
+ case Instruction::Load:
+ // A load here means one of two things: a load of undef from a global,
+ // a load from an unknown pointer. Either way, having it return undef
+ // is okay.
+ break;
+ case Instruction::ICmp:
+ // X == undef -> undef. Other comparisons get more complicated.
+ if (cast<ICmpInst>(I)->isEquality())
+ break;
+ markOverdefined(I);
+ return true;
+ default:
+ // If we don't know what should happen here, conservatively mark it
// overdefined.
markOverdefined(I);
return true;
Modified: llvm/trunk/test/Transforms/SCCP/undef-resolve.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SCCP/undef-resolve.ll?rev=137777&r1=137776&r2=137777&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/SCCP/undef-resolve.ll (original)
+++ llvm/trunk/test/Transforms/SCCP/undef-resolve.ll Tue Aug 16 17:06:31 2011
@@ -104,3 +104,60 @@
bb1: ; preds = %bb1.us-lcssa, %bb1.us-lcssa.us
ret i32 0
}
+
+; Make sure SCCP honors the xor "idiom"
+; rdar://9956541
+define i32 @test3() {
+ %t = xor i32 undef, undef
+ ret i32 %t
+; CHECK: @test3
+; CHECK: ret i32 0
+}
+
+; Be conservative with FP ops
+define double @test4(double %x) {
+ %t = fadd double %x, undef
+ ret double %t
+; CHECK: @test4
+; CHECK: fadd double %x, undef
+}
+
+; Make sure casts produce a possible value
+define i32 @test5() {
+ %t = sext i8 undef to i32
+ ret i32 %t
+; CHECK: @test5
+; CHECK: ret i32 0
+}
+
+; Make sure ashr produces a possible value
+define i32 @test6() {
+ %t = ashr i32 undef, 31
+ ret i32 %t
+; CHECK: @test6
+; CHECK: ret i32 -1
+}
+
+; Make sure lshr produces a possible value
+define i32 @test7() {
+ %t = lshr i32 undef, 31
+ ret i32 %t
+; CHECK: @test7
+; CHECK: ret i32 0
+}
+
+; icmp eq with undef simplifies to undef
+define i1 @test8() {
+ %t = icmp eq i32 undef, -1
+ ret i1 %t
+; CHECK: @test8
+; CHECK: ret i1 undef
+}
+
+; Make sure we don't conclude that relational comparisons simplify to undef
+define i1 @test9() {
+ %t = icmp ugt i32 undef, -1
+ ret i1 %t
+; CHECK: @test9
+; CHECK: icmp ugt
+}
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