[NewGVN] Make NewGVN aware of aligned_alloc

[bondhugula]

Summary

Make the New GVN pass aware of aligned_alloc.

Signed-off-by: Uday Bondhugula <[e-mail]>

Depends on D76975.

[bondhugula]

Add test case

[fhahn]

Please prefix the commit message with something like [NewGVN]

[bondhugula]

In D76976#1948652, @fhahn wrote:

Please prefix the commit message with something like [NewGVN]

Even if NewGVN already appears in the title? Thanks.

llvm/lib/Transforms/Scalar/NewGVN.cpp

NewGVN::performSymbolicLoadCoercion(Type *LoadType, Value *LoadPtr,
   // by the dependent instruction.
   if (LoadPtr != lookupOperandLeader(DepInst) &&
       !AA->isMustAlias(LoadPtr, DepInst))
     return nullptr;
   // If this load really doesn't depend on anything, then we must be loading an
   // undef value.  This can happen when loading for a fresh allocation with no
   // intervening stores, for example.  Note that this is only true in the case
   // that the result of the allocation is pointer equal to the load ptr.
-  if (isa<AllocaInst>(DepInst) || isMallocLikeFn(DepInst, TLI)) {
+  if (isa<AllocaInst>(DepInst) || isMallocLikeFn(DepInst, TLI) ||
+      isAlignedAllocLikeFn(DepInst, TLI)) {
     return createConstantExpression(UndefValue::get(LoadType));
   }
   // If this load occurs either right after a lifetime begin,
   // then the loaded value is undefined.
   else if (auto *II = dyn_cast<IntrinsicInst>(DepInst)) {
     if (II->getIntrinsicID() == Intrinsic::lifetime_start)
       return createConstantExpression(UndefValue::get(LoadType));
   }

llvm/test/Transforms/NewGVN/malloc-load-removal.ll

 ; CHECK-LABEL: @test2(
 ; CHECK-NOT: load
 ; CHECK-NOT: icmp
 
 ; CHECK_NO_LIBCALLS-LABEL: @test2(
 ; CHECK_NO_LIBCALLS: load
 ; CHECK_NO_LIBCALLS: icmp
 }
+
+declare i8* @aligned_alloc(i64, i64) nounwind
+
+define noalias i8* @test3() nounwind uwtable ssp {
+entry:
+  %call = tail call i8* @aligned_alloc(i64 256, i64 32) nounwind
+  %0 = load i8, i8* %call, align 32
+  %tobool = icmp eq i8 %0, 0
+  br i1 %tobool, label %if.end, label %if.then
+
+if.then:                                          ; preds = %entry
+  store i8 0, i8* %call, align 1
+  br label %if.end
+
+if.end:                                           ; preds = %if.then, %entry
+  ret i8* %call
+
+; CHECK-LABEL: @test3(
+; CHECK-NOT: load
+; CHECK-NOT: icmp
+
+; CHECK_NO_LIBCALLS-LABEL: @test3(
+; CHECK_NO_LIBCALLS: load
+; CHECK_NO_LIBCALLS: icmp
+}