[ARM CGP] Fix ConvertTruncs

ConvertTruncs is used to replace a trunc for an AND mask, however
this function wasn't working as expected. By performing the change
later, we can create a wide type integer mask instead of a narrow -1
value, which could then be simply removed (incorrectly). Because we
now perform this action later, it's necessary to cache the trunc type
before we perform the promotion.

Differential Revision: https://reviews.llvm.org/D57686

llvm-svn: 354108

Author: sparker-arm

llvm/lib/Target/ARM/ARMCodeGenPrepare.cpp

@@ -686,6 +686,7 @@ void IRPromoter::TruncateSinks() {
 }
 
 void IRPromoter::Cleanup() {
+  LLVM_DEBUG(dbgs() << "ARM CGP: Cleanup..\n");
   // Some zexts will now have become redundant, along with their trunc
   // operands, so remove them
   for (auto V : *Visited) {
@@ -729,19 +730,21 @@ void IRPromoter::Cleanup() {
 }
 
 void IRPromoter::ConvertTruncs() {
+  LLVM_DEBUG(dbgs() << "ARM CGP: Converting truncs..\n");
   IRBuilder<> Builder{Ctx};
 
   for (auto *V : *Visited) {
     if (!isa<TruncInst>(V) || Sources->count(V))
       continue;
 
     auto *Trunc = cast<TruncInst>(V);
-    assert(LessThanTypeSize(Trunc) && "expected narrow trunc");
-
     Builder.SetInsertPoint(Trunc);
-    unsigned NumBits =
-      cast<IntegerType>(Trunc->getType())->getScalarSizeInBits();
-    ConstantInt *Mask = ConstantInt::get(Ctx, APInt::getMaxValue(NumBits));
+    IntegerType *SrcTy = cast<IntegerType>(Trunc->getOperand(0)->getType());
+    IntegerType *DestTy = cast<IntegerType>(TruncTysMap[Trunc][0]);
+
+    unsigned NumBits = DestTy->getScalarSizeInBits();
+    ConstantInt *Mask =
+      ConstantInt::get(SrcTy, APInt::getMaxValue(NumBits).getZExtValue());
     Value *Masked = Builder.CreateAnd(Trunc->getOperand(0), Mask);
 
     if (auto *I = dyn_cast<Instruction>(Masked))
@@ -783,6 +786,12 @@ void IRPromoter::Mutate(Type *OrigTy,
         TruncTysMap[I].push_back(I->getOperand(i)->getType());
     }
   }
+  for (auto *V : Visited) {
+    if (!isa<TruncInst>(V) || Sources.count(V))
+      continue;
+    auto *Trunc = cast<TruncInst>(V);
+    TruncTysMap[Trunc].push_back(Trunc->getDestTy());
+  }
 
   // Convert adds and subs using negative immediates to equivalent instructions
   // that use positive constants.
@@ -791,14 +800,14 @@ void IRPromoter::Mutate(Type *OrigTy,
   // Insert zext instructions between sources and their users.
   ExtendSources();
 
-  // Convert any truncs, that aren't sources, into AND masks.
-  ConvertTruncs();
-
   // Promote visited instructions, mutating their types in place. Also insert
   // DSP intrinsics, if enabled, for adds and subs which would be unsafe to
   // promote.
   PromoteTree();
 
+  // Convert any truncs, that aren't sources, into AND masks.
+  ConvertTruncs();
+
   // Insert trunc instructions for use by calls, stores etc...
   TruncateSinks();
 

llvm/test/CodeGen/ARM/CGP/arm-cgp-calls.ll

@@ -201,7 +201,7 @@ exit:
 }
 
 ; CHECK-LABEL: promote_arg_pass_to_call
-; CHECK-NOT: uxt
+; CHECK: uxtb
 define i16 @promote_arg_pass_to_call(i16 zeroext %arg1, i16 zeroext %arg2) {
   %conv = add nuw i16 %arg1, 15
   %mul = mul nuw nsw i16 %conv, 3