[llvm-commits] [llvm] r57387 - in /llvm/trunk: lib/Transforms/Scalar/InstructionCombining.cpp test/Transforms/InstCombine/2008-10-11-DivCompareFold.ll
Chris Lattner
sabre at nondot.org
Sat Oct 11 15:55:01 PDT 2008
Author: lattner
Date: Sat Oct 11 17:55:00 2008
New Revision: 57387
URL: http://llvm.org/viewvc/llvm-project?rev=57387&view=rev
Log:
Fix PR2697 by rewriting the '(X / pos) op neg' logic. This also changes
a couple other cases for clarity, but shouldn't affect correctness.
Patch by Eli Friedman!
Added:
llvm/trunk/test/Transforms/InstCombine/2008-10-11-DivCompareFold.ll
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=57387&r1=57386&r2=57387&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp Sat Oct 11 17:55:00 2008
@@ -5784,6 +5784,11 @@
return 0;
if (DivRHS->isZero())
return 0; // The ProdOV computation fails on divide by zero.
+ if (DivIsSigned && DivRHS->isAllOnesValue())
+ return 0; // The overflow computation also screws up here
+ if (DivRHS->isOne())
+ return 0; // Not worth bothering, and eliminates some funny cases
+ // with INT_MIN.
// Compute Prod = CI * DivRHS. We are essentially solving an equation
// of form X/C1=C2. We solve for X by multiplying C1 (DivRHS) and
@@ -5810,7 +5815,6 @@
int LoOverflow = 0, HiOverflow = 0;
ConstantInt *LoBound = 0, *HiBound = 0;
-
if (!DivIsSigned) { // udiv
// e.g. X/5 op 3 --> [15, 20)
LoBound = Prod;
@@ -5829,11 +5833,13 @@
HiOverflow = AddWithOverflow(HiBound, Prod, DivRHS, true);
} else { // (X / pos) op neg
// e.g. X/5 op -3 --> [-15-4, -15+1) --> [-19, -14)
- Constant *DivRHSH = ConstantExpr::getNeg(SubOne(DivRHS));
- LoOverflow = AddWithOverflow(LoBound, Prod,
- cast<ConstantInt>(DivRHSH), true) ? -1 : 0;
HiBound = AddOne(Prod);
- HiOverflow = ProdOV ? -1 : 0;
+ LoOverflow = HiOverflow = ProdOV ? -1 : 0;
+ if (!LoOverflow) {
+ ConstantInt* DivNeg = cast<ConstantInt>(ConstantExpr::getNeg(DivRHS));
+ LoOverflow = AddWithOverflow(LoBound, HiBound, DivNeg,
+ true) ? -1 : 0;
+ }
}
} else if (DivRHS->getValue().isNegative()) { // Divisor is < 0.
if (CmpRHSV == 0) { // (X / neg) op 0
@@ -5846,14 +5852,13 @@
}
} else if (CmpRHSV.isStrictlyPositive()) { // (X / neg) op pos
// e.g. X/-5 op 3 --> [-19, -14)
+ HiBound = AddOne(Prod);
HiOverflow = LoOverflow = ProdOV ? -1 : 0;
if (!LoOverflow)
- LoOverflow = AddWithOverflow(LoBound, Prod, AddOne(DivRHS), true) ?-1:0;
- HiBound = AddOne(Prod);
+ LoOverflow = AddWithOverflow(LoBound, HiBound, DivRHS, true) ? -1 : 0;
} else { // (X / neg) op neg
- // e.g. X/-5 op -3 --> [15, 20)
- LoBound = Prod;
- LoOverflow = HiOverflow = ProdOV ? 1 : 0;
+ LoBound = Prod; // e.g. X/-5 op -3 --> [15, 20)
+ LoOverflow = HiOverflow = ProdOV;
if (!HiOverflow)
HiOverflow = SubWithOverflow(HiBound, Prod, DivRHS, true);
}
Added: llvm/trunk/test/Transforms/InstCombine/2008-10-11-DivCompareFold.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/2008-10-11-DivCompareFold.ll?rev=57387&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/2008-10-11-DivCompareFold.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/2008-10-11-DivCompareFold.ll Sat Oct 11 17:55:00 2008
@@ -0,0 +1,8 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep {ret i1 false}
+; PR2697
+
+define i1 @x(i32 %x) nounwind {
+ %div = sdiv i32 %x, 65536 ; <i32> [#uses=1]
+ %cmp = icmp slt i32 %div, -65536
+ ret i1 %cmp
+}
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