Reapply r237539 with a fix for the Chromium build.
Make sure if we're truncating a constant that would then be sign extended
that the sign extension of the truncated constant is the same as the
original constant.
> Canonicalize min/max expressions correctly.
>
> This patch introduces a canonical form for min/max idioms where one operand
> is extended or truncated. This often happens when the other operand is a
> constant. For example:
>
> %1 = icmp slt i32 %a, i32 0
> %2 = sext i32 %a to i64
> %3 = select i1 %1, i64 %2, i64 0
>
> Would now be canonicalized into:
>
> %1 = icmp slt i32 %a, i32 0
> %2 = select i1 %1, i32 %a, i32 0
> %3 = sext i32 %2 to i64
>
> This builds upon a patch posted by David Majenemer
> (https://www.marc.info/?l=llvm-commits&m=143008038714141&w=2). That pass
> passively stopped instcombine from ruining canonical patterns. This
> patch additionally actively makes instcombine canonicalize too.
>
> Canonicalization of expressions involving a change in type from int->fp
> or fp->int are not yet implemented.
llvm-svn: 237821
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 53ab81d..b060453 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -714,6 +714,22 @@
return nullptr;
}
+ // Test if a CmpInst instruction is used exclusively by a select as
+ // part of a minimum or maximum operation. If so, refrain from doing
+ // any other folding. This helps out other analyses which understand
+ // non-obfuscated minimum and maximum idioms, such as ScalarEvolution
+ // and CodeGen. And in this case, at least one of the comparison
+ // operands has at least one user besides the compare (the select),
+ // which would often largely negate the benefit of folding anyway.
+ if (auto *CI = dyn_cast<CmpInst>(SI->getCondition())) {
+ if (CI->hasOneUse()) {
+ Value *Op0 = CI->getOperand(0), *Op1 = CI->getOperand(1);
+ if ((SI->getOperand(1) == Op0 && SI->getOperand(2) == Op1) ||
+ (SI->getOperand(2) == Op0 && SI->getOperand(1) == Op1))
+ return nullptr;
+ }
+ }
+
Value *SelectTrueVal = FoldOperationIntoSelectOperand(Op, TV, this);
Value *SelectFalseVal = FoldOperationIntoSelectOperand(Op, FV, this);
@@ -723,7 +739,6 @@
return nullptr;
}
-
/// FoldOpIntoPhi - Given a binary operator, cast instruction, or select which
/// has a PHI node as operand #0, see if we can fold the instruction into the
/// PHI (which is only possible if all operands to the PHI are constants).