[PATCH] D47144: [InstCombine] Fix PR37526: MinMax patterns produce an infinite loop.

[Alexey Bataev via Phabricator via llvm-commits]

ABataev created this revision.
ABataev added reviewers: spatel, RKSimon, hfinkel.

This patch fixes PR37526 by simplifying the newly generated LoadInst
instructions. If the pointer address is a bitcast from the pointer to
the NewType, we can just remove this extra bitcast instead of creating
the new one. This fixes the PR37526 + may speed up the whole compilation
process.


Repository:
  rL LLVM

https://reviews.llvm.org/D47144

Files:
  lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
  test/Transforms/InstCombine/PR37526.ll


Index: test/Transforms/InstCombine/PR37526.ll
===================================================================
--- /dev/null
+++ test/Transforms/InstCombine/PR37526.ll
@@ -0,0 +1,43 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -instcombine -S < %s | FileCheck %s
+
+%struct.x5 = type { i32 (...)**, i32, i32 }
+
+define void @repro(%struct.x5*, %struct.x5* %x12, %struct.x5* %x13) {
+; CHECK-LABEL: @repro(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[X37_I_I:%.*]] = getelementptr inbounds [[STRUCT_X5:%.*]], %struct.x5* [[X12:%.*]], i64 0, i32 1
+; CHECK-NEXT:    [[X37_I:%.*]] = getelementptr inbounds [[STRUCT_X5]], %struct.x5* [[X13:%.*]], i64 0, i32 1
+; CHECK-NEXT:    br label [[FOR_COND:%.*]]
+; CHECK:       for.cond:
+; CHECK-NEXT:    [[X14_0:%.*]] = phi %struct.x5* [ undef, [[ENTRY:%.*]] ], [ [[INCDEC_PTR:%.*]], [[FOR_COND]] ]
+; CHECK-NEXT:    [[INCDEC_PTR]] = getelementptr inbounds [[STRUCT_X5]], %struct.x5* [[X14_0]], i64 -1
+; CHECK-NEXT:    [[TMP1:%.*]] = load i32, i32* [[X37_I_I]], align 4
+; CHECK-NEXT:    [[X37_I2_I:%.*]] = getelementptr inbounds [[STRUCT_X5]], %struct.x5* [[X14_0]], i64 -1, i32 1
+; CHECK-NEXT:    [[TMP2:%.*]] = load i32, i32* [[X37_I2_I]], align 4
+; CHECK-NEXT:    [[CMP_I:%.*]] = icmp slt i32 [[TMP1]], [[TMP2]]
+; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 [[CMP_I]], i32* [[X37_I2_I]], i32* [[X37_I_I]]
+; CHECK-NEXT:    [[STOREMERGE1:%.*]] = load i32, i32* [[SPEC_SELECT]], align 8
+; CHECK-NEXT:    store i32 [[STOREMERGE1]], i32* [[X37_I]], align 8
+; CHECK-NEXT:    br label [[FOR_COND]]
+;
+entry:
+  %x37.i.i = getelementptr inbounds %struct.x5, %struct.x5* %x12, i64 0, i32 1
+  %x37.i = getelementptr inbounds %struct.x5, %struct.x5* %x13, i64 0, i32 1
+  %1 = bitcast i32* %x37.i to i64*
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.cond, %entry
+  %x14.0 = phi %struct.x5* [ undef, %entry ], [ %incdec.ptr, %for.cond ]
+  %incdec.ptr = getelementptr inbounds %struct.x5, %struct.x5* %x14.0, i64 -1
+  %2 = load i32, i32* %x37.i.i, align 4
+  %x37.i2.i = getelementptr inbounds %struct.x5, %struct.x5* %x14.0, i64 -1, i32 1
+  %3 = load i32, i32* %x37.i2.i, align 4
+  %cmp.i = icmp slt i32 %2, %3
+  %spec.select = select i1 %cmp.i, i32* %x37.i2.i, i32* %x37.i.i
+  %storemerge.in = bitcast i32* %spec.select to i64*
+  %storemerge = load i64, i64* %storemerge.in, align 8
+  store i64 %storemerge, i64* %1, align 8
+  br label %for.cond
+}
+
Index: lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -453,15 +453,24 @@
                                       const Twine &Suffix = "") {
   assert((!LI.isAtomic() || isSupportedAtomicType(NewTy)) &&
          "can't fold an atomic load to requested type");
-  
+
   Value *Ptr = LI.getPointerOperand();
   unsigned AS = LI.getPointerAddressSpace();
   SmallVector<std::pair<unsigned, MDNode *>, 8> MD;
   LI.getAllMetadata(MD);
 
+  Value *NewPtr = nullptr;
+  if (auto *BC = dyn_cast<BitCastInst>(Ptr)) {
+    Value *Op0 = BC->getOperand(0);
+    if (Op0->getType()->getPointerElementType() == NewTy &&
+        Op0->getType()->getPointerAddressSpace() == AS)
+      NewPtr = BC->getOperand(0);
+  }
+  if (!NewPtr)
+    NewPtr = IC.Builder.CreateBitCast(Ptr, NewTy->getPointerTo(AS));
+
   LoadInst *NewLoad = IC.Builder.CreateAlignedLoad(
-      IC.Builder.CreateBitCast(Ptr, NewTy->getPointerTo(AS)),
-      LI.getAlignment(), LI.isVolatile(), LI.getName() + Suffix);
+      NewPtr, LI.getAlignment(), LI.isVolatile(), LI.getName() + Suffix);
   NewLoad->setAtomic(LI.getOrdering(), LI.getSyncScopeID());
   MDBuilder MDB(NewLoad->getContext());
   for (const auto &MDPair : MD) {


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