[InstCombine] Check type compatibility in indexed load fold

This fold could use a rewrite to an offset-based implementation,
but for now make sure it doesn't crash with opaque pointers.

Author: nikic

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

@@ -105,10 +105,14 @@ static bool isSignTest(ICmpInst::Predicate &Pred, const APInt &C) {
 ///
 /// If AndCst is non-null, then the loaded value is masked with that constant
 /// before doing the comparison. This handles cases like "A[i]&4 == 0".
-Instruction *
-InstCombinerImpl::foldCmpLoadFromIndexedGlobal(GetElementPtrInst *GEP,
-                                               GlobalVariable *GV, CmpInst &ICI,
-                                               ConstantInt *AndCst) {
+Instruction *InstCombinerImpl::foldCmpLoadFromIndexedGlobal(
+    LoadInst *LI, GetElementPtrInst *GEP, GlobalVariable *GV, CmpInst &ICI,
+    ConstantInt *AndCst) {
+  if (LI->isVolatile() || LI->getType() != GEP->getResultElementType() ||
+      GV->getValueType() != GEP->getSourceElementType() ||
+      !GV->isConstant() || !GV->hasDefinitiveInitializer())
+    return nullptr;
+
   Constant *Init = GV->getInitializer();
   if (!isa<ConstantArray>(Init) && !isa<ConstantDataArray>(Init))
     return nullptr;
@@ -1865,15 +1869,13 @@ Instruction *InstCombinerImpl::foldICmpAndConstant(ICmpInst &Cmp,
   // Try to optimize things like "A[i] & 42 == 0" to index computations.
   Value *X = And->getOperand(0);
   Value *Y = And->getOperand(1);
-  if (auto *LI = dyn_cast<LoadInst>(X))
-    if (auto *GEP = dyn_cast<GetElementPtrInst>(LI->getOperand(0)))
-      if (auto *GV = dyn_cast<GlobalVariable>(GEP->getOperand(0)))
-        if (GV->isConstant() && GV->hasDefinitiveInitializer() &&
-            !LI->isVolatile() && isa<ConstantInt>(Y)) {
-          ConstantInt *C2 = cast<ConstantInt>(Y);
-          if (Instruction *Res = foldCmpLoadFromIndexedGlobal(GEP, GV, Cmp, C2))
+  if (auto *C2 = dyn_cast<ConstantInt>(Y))
+    if (auto *LI = dyn_cast<LoadInst>(X))
+      if (auto *GEP = dyn_cast<GetElementPtrInst>(LI->getOperand(0)))
+        if (auto *GV = dyn_cast<GlobalVariable>(GEP->getOperand(0)))
+          if (Instruction *Res =
+                  foldCmpLoadFromIndexedGlobal(LI, GEP, GV, Cmp, C2))
             return Res;
-        }
 
   if (!Cmp.isEquality())
     return nullptr;
@@ -3476,13 +3478,11 @@ Instruction *InstCombinerImpl::foldICmpInstWithConstantNotInt(ICmpInst &I) {
   case Instruction::Load:
     // Try to optimize things like "A[i] > 4" to index computations.
     if (GetElementPtrInst *GEP =
-            dyn_cast<GetElementPtrInst>(LHSI->getOperand(0))) {
+            dyn_cast<GetElementPtrInst>(LHSI->getOperand(0)))
       if (GlobalVariable *GV = dyn_cast<GlobalVariable>(GEP->getOperand(0)))
-        if (GV->isConstant() && GV->hasDefinitiveInitializer() &&
-            !cast<LoadInst>(LHSI)->isVolatile())
-          if (Instruction *Res = foldCmpLoadFromIndexedGlobal(GEP, GV, I))
-            return Res;
-    }
+        if (Instruction *Res =
+                foldCmpLoadFromIndexedGlobal(cast<LoadInst>(LHSI), GEP, GV, I))
+          return Res;
     break;
   }
 
@@ -6632,10 +6632,9 @@ Instruction *InstCombinerImpl::visitFCmpInst(FCmpInst &I) {
     case Instruction::Load:
       if (auto *GEP = dyn_cast<GetElementPtrInst>(LHSI->getOperand(0)))
         if (auto *GV = dyn_cast<GlobalVariable>(GEP->getOperand(0)))
-          if (GV->isConstant() && GV->hasDefinitiveInitializer() &&
-              !cast<LoadInst>(LHSI)->isVolatile())
-            if (Instruction *Res = foldCmpLoadFromIndexedGlobal(GEP, GV, I))
-              return Res;
+          if (Instruction *Res = foldCmpLoadFromIndexedGlobal(
+                  cast<LoadInst>(LHSI), GEP, GV, I))
+            return Res;
       break;
   }
   }

llvm/lib/Transforms/InstCombine/InstCombineInternal.h

@@ -652,7 +652,8 @@ class LLVM_LIBRARY_VISIBILITY InstCombinerImpl final
                            ICmpInst::Predicate Cond, Instruction &I);
   Instruction *foldAllocaCmp(ICmpInst &ICI, const AllocaInst *Alloca,
                              const Value *Other);
-  Instruction *foldCmpLoadFromIndexedGlobal(GetElementPtrInst *GEP,
+  Instruction *foldCmpLoadFromIndexedGlobal(LoadInst *LI,
+                                            GetElementPtrInst *GEP,
                                             GlobalVariable *GV, CmpInst &ICI,
                                             ConstantInt *AndCst = nullptr);
   Instruction *foldFCmpIntToFPConst(FCmpInst &I, Instruction *LHSI,

llvm/test/Transforms/InstCombine/opaque-ptr.ll

@@ -305,3 +305,42 @@ define i1 @cmp_gep_same_base_different_type(ptr %ptr, i64 %idx1, i64 %idx2) {
   %cmp = icmp ult ptr %gep1, %gep2
   ret i1 %cmp
 }
+
+@ary = constant [4 x i8] [i8 1, i8 2, i8 3, i8 4]
+
+define i1 @cmp_load_gep_global(i64 %idx) {
+; CHECK-LABEL: @cmp_load_gep_global(
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i64 [[IDX:%.*]], 2
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %gep = getelementptr [4 x i8], ptr @ary, i64 0, i64 %idx
+  %load = load i8, ptr %gep
+  %cmp = icmp eq i8 %load, 3
+  ret i1 %cmp
+}
+
+define i1 @cmp_load_gep_global_different_load_type(i64 %idx) {
+; CHECK-LABEL: @cmp_load_gep_global_different_load_type(
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr [4 x i8], ptr @ary, i64 0, i64 [[IDX:%.*]]
+; CHECK-NEXT:    [[LOAD:%.*]] = load i16, ptr [[GEP]], align 2
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i16 [[LOAD]], 3
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %gep = getelementptr [4 x i8], ptr @ary, i64 0, i64 %idx
+  %load = load i16, ptr %gep
+  %cmp = icmp eq i16 %load, 3
+  ret i1 %cmp
+}
+
+define i1 @cmp_load_gep_global_different_gep_type(i64 %idx) {
+; CHECK-LABEL: @cmp_load_gep_global_different_gep_type(
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr [4 x i16], ptr @ary, i64 0, i64 [[IDX:%.*]]
+; CHECK-NEXT:    [[LOAD:%.*]] = load i16, ptr [[GEP]], align 2
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i16 [[LOAD]], 3
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %gep = getelementptr [4 x i16], ptr @ary, i64 0, i64 %idx
+  %load = load i16, ptr %gep
+  %cmp = icmp eq i16 %load, 3
+  ret i1 %cmp
+}