Reapply r237539 with a fix for the Chromium build.

[oota-llvm.git] / lib / Transforms / InstCombine / InstCombineCasts.cpp

diff --git a/lib/Transforms/InstCombine/InstCombineCasts.cpp b/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 9c2bc34f678fd71f53b2a78b40ab0eba3cc24aad..48ab0eb2c1b9227abc39fd2b32c2c100d1e2ab43 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -435,6 +435,15 @@ Instruction *InstCombiner::visitTrunc(TruncInst &CI) {
   if (Instruction *Result = commonCastTransforms(CI))
     return Result;
 
+  // Test if the trunc is the user of a select which is part of a
+  // minimum or maximum operation. If so, don't do any more simplification.
+  // Even simplifying demanded bits can break the canonical form of a 
+  // min/max.
+  Value *LHS, *RHS;
+  if (SelectInst *SI = dyn_cast<SelectInst>(CI.getOperand(0)))
+    if (matchSelectPattern(SI, LHS, RHS) != SPF_UNKNOWN)
+      return nullptr;
+  
   // See if we can simplify any instructions used by the input whose sole
   // purpose is to compute bits we don't care about.
   if (SimplifyDemandedInstructionBits(CI))