forked from OSchip/llvm-project
[SCCP] Teach the pass about `mul %x 0` even if %x is overdefined.
The motivating example is: extern int patatino; int goo() { int x = 0; for (int i = 0; i < 1000000; ++i) { x *= patatino; } return x; } Currently SCCP will not realize that this function returns always zero, therefore will try to unroll and vectorize the loop at -O3 producing an awful lot of (useless) code. With this change, it will just produce: 0000000000000000 <g>: xor %eax,%eax retq llvm-svn: 289175
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@ -916,7 +916,8 @@ void SCCPSolver::visitBinaryOperator(Instruction &I) {
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// If this is an AND or OR with 0 or -1, it doesn't matter that the other
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// operand is overdefined.
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if (I.getOpcode() == Instruction::And || I.getOpcode() == Instruction::Or) {
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if (I.getOpcode() == Instruction::And || I.getOpcode() == Instruction::Mul ||
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I.getOpcode() == Instruction::Or) {
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LatticeVal *NonOverdefVal = nullptr;
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if (!V1State.isOverdefined())
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NonOverdefVal = &V1State;
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@ -927,8 +928,10 @@ void SCCPSolver::visitBinaryOperator(Instruction &I) {
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if (NonOverdefVal->isUnknown())
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return;
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if (I.getOpcode() == Instruction::And) {
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if (I.getOpcode() == Instruction::And ||
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I.getOpcode() == Instruction::Mul) {
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// X and 0 = 0
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// X * 0 = 0
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if (NonOverdefVal->getConstant()->isNullValue())
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return markConstant(IV, &I, NonOverdefVal->getConstant());
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} else {
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@ -1,6 +1,6 @@
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; RUN: opt < %s -sccp -S | FileCheck %s
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; Test that SCCP has basic knowledge of when and/or nuke overdefined values.
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; Test that SCCP has basic knowledge of when and/or/mul nuke overdefined values.
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; CHECK-LABEL: test
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; CHECK: ret i32 0
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@ -29,3 +29,10 @@ define i32 @test4(i32 %X) {
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%Y = or i32 %X, undef
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ret i32 %Y
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}
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; CHECK-LABEL: test5
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; CHECK: ret i32 0
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define i32 @test5(i32 %foo) {
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%patatino = mul i32 %foo, undef
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ret i32 %patatino
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}
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