Handle IntToPtr in isBytewiseValue

Summary:
This helps with more efficient use of memset for pattern initialization

From @pcc prototype for -ftrivial-auto-var-init=pattern optimizations

Binary size change on CTMark, (with -fuse-ld=lld -Wl,--icf=all, similar results with default linker options)
```
                   master           patch      diff
Os           8.238864e+05    8.238864e+05       0.0
O3           1.054797e+06    1.054797e+06       0.0
Os zero      8.292384e+05    8.292384e+05       0.0
O3 zero      1.062626e+06    1.062626e+06       0.0
Os pattern   8.579712e+05    8.338048e+05 -0.030299
O3 pattern   1.090502e+06    1.067574e+06 -0.020481
```

Zero vs Pattern on master
```
               zero       pattern      diff
Os     8.292384e+05  8.579712e+05  0.036578
O3     1.062626e+06  1.090502e+06  0.025124
```

Zero vs Pattern with the patch
```
               zero       pattern      diff
Os     8.292384e+05  8.338048e+05  0.003333
O3     1.062626e+06  1.067574e+06  0.003193
```

Reviewers: pcc, eugenis

Subscribers: hiraditya, cfe-commits, llvm-commits

Tags: #clang, #llvm

Differential Revision: https://reviews.llvm.org/D63967

llvm-svn: 365858

clang/test/CodeGenCXX/auto-var-init.cpp

@@ -1042,14 +1042,8 @@ TEST_UNINIT(intptr4, int*[4]);
 // CHECK:            %uninit = alloca [4 x i32*], align
 // CHECK-NEXT:       call void @{{.*}}used{{.*}}%uninit)
 // PATTERN-O1-LABEL: @test_intptr4_uninit()
-// PATTERN-O1:       %1 = getelementptr inbounds [4 x i32*], [4 x i32*]* %uninit, i64 0, i64 0
+// PATTERN-O1:       %1 = bitcast [4 x i32*]* %uninit to i8*
-// PATTERN-O1-NEXT:  store i32* inttoptr (i64 -6148914691236517206 to i32*), i32** %1, align 16
+// PATTERN-O1-NEXT:  call void @llvm.memset.p0i8.i64(i8* nonnull align 16 %1, i8 -86, i64 32, i1 false)
-// PATTERN-O1-NEXT:  %2 = getelementptr inbounds [4 x i32*], [4 x i32*]* %uninit, i64 0, i64 1
-// PATTERN-O1-NEXT:  store i32* inttoptr (i64 -6148914691236517206 to i32*), i32** %2, align 8
-// PATTERN-O1-NEXT:  %3 = getelementptr inbounds [4 x i32*], [4 x i32*]* %uninit, i64 0, i64 2
-// PATTERN-O1-NEXT:  store i32* inttoptr (i64 -6148914691236517206 to i32*), i32** %3, align 16
-// PATTERN-O1-NEXT:  %4 = getelementptr inbounds [4 x i32*], [4 x i32*]* %uninit, i64 0, i64 3
-// PATTERN-O1-NEXT:  store i32* inttoptr (i64 -6148914691236517206 to i32*), i32** %4, align 8
 // ZERO-LABEL:       @test_intptr4_uninit()
 // ZERO:             call void @llvm.memset{{.*}}, i8 0,
 

llvm/lib/Analysis/ValueTracking.cpp

@@ -3218,6 +3218,17 @@ Value *llvm::isBytewiseValue(Value *V, const DataLayout &DL) {
     }
   }
 
+  if (auto *CE = dyn_cast<ConstantExpr>(C)) {
+    if (CE->getOpcode() == Instruction::IntToPtr) {
+      auto PS = DL.getPointerSizeInBits(
+          cast<PointerType>(CE->getType())->getAddressSpace());
+      return isBytewiseValue(
+          ConstantExpr::getIntegerCast(CE->getOperand(0),
+                                       Type::getIntNTy(Ctx, PS), false),
+          DL);
+    }
+  }
+
   auto Merge = [&](Value *LHS, Value *RHS) -> Value * {
     if (LHS == RHS)
       return LHS;

llvm/unittests/Analysis/ValueTrackingTest.cpp

@@ -794,11 +794,11 @@ const std::pair<const char *, const char *> IsBytewiseValueTests[] = {
         "i16* inttoptr (i64 0 to i16*)",
     },
     {
-        "",
+        "i8 -1",
         "i16* inttoptr (i64 -1 to i16*)",
     },
     {
-        "",
+        "i8 -86",
         "i16* inttoptr (i64 -6148914691236517206 to i16*)",
     },
     {
@@ -806,7 +806,7 @@ const std::pair<const char *, const char *> IsBytewiseValueTests[] = {
         "i16* inttoptr (i48 -1 to i16*)",
     },
     {
-        "",
+        "i8 -1",
         "i16* inttoptr (i96 -1 to i16*)",
     },
     {