[InstCombine] rename SimplifyDivRemOfSelect to be clearer, add comments, simplify code; NFCI
There's at least one bug here - this code can fail with vector types (PR34856).
It's also being called for FREM; I'm still trying to understand how that is valid.
llvm-svn: 315127
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
index 6b7bcd9..46f8611 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -277,7 +277,7 @@
Instruction *visitURem(BinaryOperator &I);
Instruction *visitSRem(BinaryOperator &I);
Instruction *visitFRem(BinaryOperator &I);
- bool SimplifyDivRemOfSelect(BinaryOperator &I);
+ bool simplifyDivRemOfSelectWithZeroOp(BinaryOperator &I);
Instruction *commonRemTransforms(BinaryOperator &I);
Instruction *commonIRemTransforms(BinaryOperator &I);
Instruction *commonDivTransforms(BinaryOperator &I);
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 0f76271..4290d8d 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -778,24 +778,23 @@
return Changed ? &I : nullptr;
}
-/// Try to fold a divide or remainder of a select instruction.
-bool InstCombiner::SimplifyDivRemOfSelect(BinaryOperator &I) {
- SelectInst *SI = cast<SelectInst>(I.getOperand(1));
-
- // div/rem X, (Cond ? 0 : Y) -> div/rem X, Y
- int NonNullOperand = -1;
- if (Constant *ST = dyn_cast<Constant>(SI->getOperand(1)))
- if (ST->isNullValue())
- NonNullOperand = 2;
- // div/rem X, (Cond ? Y : 0) -> div/rem X, Y
- if (Constant *ST = dyn_cast<Constant>(SI->getOperand(2)))
- if (ST->isNullValue())
- NonNullOperand = 1;
-
- if (NonNullOperand == -1)
+/// Fold a divide or remainder with a select instruction divisor when one of the
+/// select operands is zero. In that case, we can use the other select operand
+/// because div/rem by zero is undefined.
+bool InstCombiner::simplifyDivRemOfSelectWithZeroOp(BinaryOperator &I) {
+ SelectInst *SI = dyn_cast<SelectInst>(I.getOperand(1));
+ if (!SI)
return false;
- Value *SelectCond = SI->getOperand(0);
+ int NonNullOperand;
+ if (match(SI->getTrueValue(), m_Zero()))
+ // div/rem X, (Cond ? 0 : Y) -> div/rem X, Y
+ NonNullOperand = 2;
+ else if (match(SI->getFalseValue(), m_Zero()))
+ // div/rem X, (Cond ? Y : 0) -> div/rem X, Y
+ NonNullOperand = 1;
+ else
+ return false;
// Change the div/rem to use 'Y' instead of the select.
I.setOperand(1, SI->getOperand(NonNullOperand));
@@ -808,6 +807,7 @@
// If the select and condition only have a single use, don't bother with this,
// early exit.
+ Value *SelectCond = SI->getCondition();
if (SI->use_empty() && SelectCond->hasOneUse())
return true;
@@ -863,7 +863,7 @@
// Handle cases involving: [su]div X, (select Cond, Y, Z)
// This does not apply for fdiv.
- if (isa<SelectInst>(Op1) && SimplifyDivRemOfSelect(I))
+ if (simplifyDivRemOfSelectWithZeroOp(I))
return &I;
if (Instruction *LHS = dyn_cast<Instruction>(Op0)) {
@@ -1458,7 +1458,7 @@
}
// Handle cases involving: rem X, (select Cond, Y, Z)
- if (isa<SelectInst>(Op1) && SimplifyDivRemOfSelect(I))
+ if (simplifyDivRemOfSelectWithZeroOp(I))
return &I;
if (isa<Constant>(Op1)) {
@@ -1613,7 +1613,7 @@
return replaceInstUsesWith(I, V);
// Handle cases involving: rem X, (select Cond, Y, Z)
- if (isa<SelectInst>(Op1) && SimplifyDivRemOfSelect(I))
+ if (simplifyDivRemOfSelectWithZeroOp(I))
return &I;
return nullptr;