ARM: override cost function to re-enable ConstantHoisting (& fix it).

At some point, ARM stopped getting any benefit from ConstantHoisting because
the pass called a different variant of getIntImmCost. Reimplementing the
correct variant revealed some problems, however:

  + ConstantHoisting was modifying switch statements. This is simply invalid,
    the cases must remain integer constants no matter the notional cost.
  + ConstantHoisting was mangling alloca instructions in the entry block. These
    should be handled by FrameLowering, so constants actually have a cost of 0.
    Worse, the resulting bitcasts meant they became dynamic allocas.

rdar://25707382

llvm-svn: 266260

2 files changed, 9 insertions, 5 deletions

diff --git a/llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp b/llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp
index c1520119ef2..932ec2d46da 100644
--- a/llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp
+++ b/llvm/lib/Target/ARM/ARMTargetTransformInfo.cpp
@@ -18,12 +18,12 @@ using namespace llvm;
 int ARMTTIImpl::getIntImmCost(const APInt &Imm, Type *Ty) {
   assert(Ty->isIntegerTy());
 
-  unsigned Bits = Ty->getPrimitiveSizeInBits();
-  if (Bits == 0 || Bits > 32)
-    return 4;
+ unsigned Bits = Ty->getPrimitiveSizeInBits();
+ if (Bits == 0 || Bits > 64)
+   return 4;
 
-  int32_t SImmVal = Imm.getSExtValue();
-  uint32_t ZImmVal = Imm.getZExtValue();
+  int64_t SImmVal = Imm.getSExtValue();
+  uint64_t ZImmVal = Imm.getZExtValue();
   if (!ST->isThumb()) {
     if ((SImmVal >= 0 && SImmVal < 65536) ||
         (ARM_AM::getSOImmVal(ZImmVal) != -1) ||
diff --git a/llvm/lib/Target/ARM/ARMTargetTransformInfo.h b/llvm/lib/Target/ARM/ARMTargetTransformInfo.h
index 7d8d2381c98..7808587c205 100644
--- a/llvm/lib/Target/ARM/ARMTargetTransformInfo.h
+++ b/llvm/lib/Target/ARM/ARMTargetTransformInfo.h
@@ -60,6 +60,10 @@ public:
   using BaseT::getIntImmCost;
   int getIntImmCost(const APInt &Imm, Type *Ty);
 
+  int getIntImmCost(unsigned Opcode, unsigned Idx, const APInt &Imm, Type *Ty) {
+    return getIntImmCost(Imm, Ty);
+  }
+
   /// @}
 
   /// \name Vector TTI Implementations