[ValueTracking][InstSimplify] Support min/max selects in computeConstantRange()

Add support for min/max flavor selects in computeConstantRange(),
which allows us to fold comparisons of a min/max against a constant
in InstSimplify. This was suggested by spatel as an alternative
approach to D59378. I've also added the infinite looping test from
that revision here.

Differential Revision: https://reviews.llvm.org/D59506

llvm-svn: 356415

1 files changed, 22 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 00123788f2f..2988043c2a2 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -5680,7 +5680,28 @@ static void setLimitsForSelectPattern(const SelectInst &SI, APInt &Lower,
     return;
   }
 
-  // TODO Handle min/max flavors.
+  const APInt *C;
+  if (!match(LHS, m_APInt(C)) && !match(RHS, m_APInt(C)))
+    return;
+
+  switch (R.Flavor) {
+    case SPF_UMIN:
+      Upper = *C + 1;
+      break;
+    case SPF_UMAX:
+      Lower = *C;
+      break;
+    case SPF_SMIN:
+      Lower = APInt::getSignedMinValue(BitWidth);
+      Upper = *C + 1;
+      break;
+    case SPF_SMAX:
+      Lower = *C;
+      Upper = APInt::getSignedMaxValue(BitWidth) + 1;
+      break;
+    default:
+      break;
+  }
 }
 
 ConstantRange llvm::computeConstantRange(const Value *V, bool UseInstrInfo) {