Avoid illegal integer promotion in fastisel

Stop folding constant adds into GEP when the type size doesn't match.
Otherwise, the adds' operands are effectively being promoted, changing the
conditions of an overflow.  Results are different when:

    sext(a) + sext(b) != sext(a + b)

Problem originally found on x86-64, but also fixed issues with ARM and PPC,
which used similar code.

<rdar://problem/15292280>

Patch by Duncan Exon Smith!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194840 91177308-0d34-0410-b5e6-96231b3b80d8

8 files changed, 102 insertions, 21 deletions

diff --git a/include/llvm/CodeGen/FastISel.h b/include/llvm/CodeGen/FastISel.h
index 0063474534..1e0ef6b545 100644
--- a/include/llvm/CodeGen/FastISel.h
+++ b/include/llvm/CodeGen/FastISel.h
@@ -358,6 +358,15 @@ protected:
     return 0;
   }
 
+  /// \brief Check if \c Add is an add that can be safely folded into \c GEP.
+  ///
+  /// \c Add can be folded into \c GEP if:
+  /// - \c Add is an add,
+  /// - \c Add's size matches \c GEP's,
+  /// - \c Add is in the same basic block as \c GEP, and
+  /// - \c Add has a constant operand.
+  bool canFoldAddIntoGEP(const User *GEP, const Value *Add);
+
 private:
   bool SelectBinaryOp(const User *I, unsigned ISDOpcode);
 
diff --git a/lib/CodeGen/SelectionDAG/FastISel.cpp b/lib/CodeGen/SelectionDAG/FastISel.cpp
index fb798c1f09..a6f746140d 100644
--- a/lib/CodeGen/SelectionDAG/FastISel.cpp
+++ b/lib/CodeGen/SelectionDAG/FastISel.cpp
@@ -1571,4 +1571,19 @@ bool FastISel::tryToFoldLoad(const LoadInst *LI, const Instruction *FoldInst) {
   return tryToFoldLoadIntoMI(User, RI.getOperandNo(), LI);
 }
 
+bool FastISel::canFoldAddIntoGEP(const User *GEP, const Value *Add) {
+  // Must be an add.
+  if (!isa<AddOperator>(Add))
+    return false;
+  // Type size needs to match.
+  if (TD.getTypeSizeInBits(GEP->getType()) !=
+      TD.getTypeSizeInBits(Add->getType()))
+    return false;
+  // Must be in the same basic block.
+  if (isa<Instruction>(Add) &&
+      FuncInfo.MBBMap[cast<Instruction>(Add)->getParent()] != FuncInfo.MBB)
+    return false;
+  // Must have a constant operand.
+  return isa<ConstantInt>(cast<AddOperator>(Add)->getOperand(1));
+}
 
diff --git a/lib/Target/ARM/ARMFastISel.cpp b/lib/Target/ARM/ARMFastISel.cpp
index f3a74c7109..a4004f32db 100644
--- a/lib/Target/ARM/ARMFastISel.cpp
+++ b/lib/Target/ARM/ARMFastISel.cpp
@@ -900,13 +900,8 @@ bool ARMFastISel::ARMComputeAddress(const Value *Obj, Address &Addr) {
               TmpOffset += CI->getSExtValue() * S;
               break;
             }
-            if (isa<AddOperator>(Op) &&
-                (!isa<Instruction>(Op) ||
-                 FuncInfo.MBBMap[cast<Instruction>(Op)->getParent()]
-                 == FuncInfo.MBB) &&
-                isa<ConstantInt>(cast<AddOperator>(Op)->getOperand(1))) {
-              // An add (in the same block) with a constant operand. Fold the
-              // constant.
+            if (canFoldAddIntoGEP(U, Op)) {
+              // A compatible add with a constant operand. Fold the constant.
               ConstantInt *CI =
               cast<ConstantInt>(cast<AddOperator>(Op)->getOperand(1));
               TmpOffset += CI->getSExtValue() * S;
diff --git a/lib/Target/PowerPC/PPCFastISel.cpp b/lib/Target/PowerPC/PPCFastISel.cpp
index 4f8e6c1a10..09117e7ded 100644
--- a/lib/Target/PowerPC/PPCFastISel.cpp
+++ b/lib/Target/PowerPC/PPCFastISel.cpp
@@ -336,13 +336,8 @@ bool PPCFastISel::PPCComputeAddress(const Value *Obj, Address &Addr) {
               TmpOffset += CI->getSExtValue() * S;
               break;
             }
-            if (isa<AddOperator>(Op) &&
-                (!isa<Instruction>(Op) ||
-                 FuncInfo.MBBMap[cast<Instruction>(Op)->getParent()]
-                 == FuncInfo.MBB) &&
-                isa<ConstantInt>(cast<AddOperator>(Op)->getOperand(1))) {
-              // An add (in the same block) with a constant operand. Fold the
-              // constant.
+            if (canFoldAddIntoGEP(U, Op)) {
+              // A compatible add with a constant operand. Fold the constant.
               ConstantInt *CI =
               cast<ConstantInt>(cast<AddOperator>(Op)->getOperand(1));
               TmpOffset += CI->getSExtValue() * S;
diff --git a/lib/Target/X86/X86FastISel.cpp b/lib/Target/X86/X86FastISel.cpp
index 928dea91b4..97f96ab72c 100644
--- a/lib/Target/X86/X86FastISel.cpp
+++ b/lib/Target/X86/X86FastISel.cpp
@@ -561,13 +561,8 @@ redo_gep:
           Disp += CI->getSExtValue() * S;
           break;
         }
-        if (isa<AddOperator>(Op) &&
-            (!isa<Instruction>(Op) ||
-             FuncInfo.MBBMap[cast<Instruction>(Op)->getParent()]
-               == FuncInfo.MBB) &&
-            isa<ConstantInt>(cast<AddOperator>(Op)->getOperand(1))) {
-          // An add (in the same block) with a constant operand. Fold the
-          // constant.
+        if (canFoldAddIntoGEP(U, Op)) {
+          // A compatible add with a constant operand. Fold the constant.
           ConstantInt *CI =
             cast<ConstantInt>(cast<AddOperator>(Op)->getOperand(1));
           Disp += CI->getSExtValue() * S;
diff --git a/test/CodeGen/ARM/fastisel-gep-promote-before-add.ll b/test/CodeGen/ARM/fastisel-gep-promote-before-add.ll
new file mode 100644
index 0000000000..a32ab6d093
--- /dev/null
+++ b/test/CodeGen/ARM/fastisel-gep-promote-before-add.ll
@@ -0,0 +1,18 @@
+; fastisel should not fold add with non-pointer bitwidth
+; sext(a) + sext(b) != sext(a + b)
+; RUN: llc -mtriple=armv7-apple-ios %s -O0 -o - | FileCheck %s
+
+define zeroext i8 @gep_promotion(i8* %ptr) nounwind uwtable ssp {
+entry:
+  %ptr.addr = alloca i8*, align 8
+  %add = add i8 64, 64 ; 0x40 + 0x40
+  %0 = load i8** %ptr.addr, align 8
+
+  ; CHECK-LABEL: _gep_promotion:
+  ; CHECK: ldrb {{r[0-9]+}}, {{\[r[0-9]+\]}}
+  %arrayidx = getelementptr inbounds i8* %0, i8 %add
+
+  %1 = load i8* %arrayidx, align 1
+  ret i8 %1
+}
+
diff --git a/test/CodeGen/PowerPC/fastisel-gep-promote-before-add.ll b/test/CodeGen/PowerPC/fastisel-gep-promote-before-add.ll
new file mode 100644
index 0000000000..4bcacf0097
--- /dev/null
+++ b/test/CodeGen/PowerPC/fastisel-gep-promote-before-add.ll
@@ -0,0 +1,17 @@
+; fastisel should not fold add with non-pointer bitwidth
+; sext(a) + sext(b) != sext(a + b)
+; RUN: llc -mtriple=powerpc64-unknown-freebsd10.0 %s -O0 -o - | FileCheck %s
+
+define zeroext i8 @gep_promotion(i8* %ptr) nounwind uwtable ssp {
+entry:
+  %ptr.addr = alloca i8*, align 8
+  %add = add i8 64, 64 ; 0x40 + 0x40
+  %0 = load i8** %ptr.addr, align 8
+
+  ; CHECK-LABEL: gep_promotion:
+  ; CHECK: lbz {{[0-9]+}}, 0({{.*}})
+  %arrayidx = getelementptr inbounds i8* %0, i8 %add
+
+  %1 = load i8* %arrayidx, align 1
+  ret i8 %1
+}
diff --git a/test/CodeGen/X86/fastisel-gep-promote-before-add.ll b/test/CodeGen/X86/fastisel-gep-promote-before-add.ll
new file mode 100644
index 0000000000..f87a34c4ab
--- /dev/null
+++ b/test/CodeGen/X86/fastisel-gep-promote-before-add.ll
@@ -0,0 +1,37 @@
+; fastisel should not fold add with non-pointer bitwidth
+; sext(a) + sext(b) != sext(a + b)
+; RUN: llc -mtriple=x86_64-apple-darwin %s -O0 -o - | FileCheck %s
+
+define zeroext i8 @gep_promotion(i8* %ptr) nounwind uwtable ssp {
+entry:
+  %ptr.addr = alloca i8*, align 8
+  %add = add i8 64, 64 ; 0x40 + 0x40
+  %0 = load i8** %ptr.addr, align 8
+
+  ; CHECK-LABEL: _gep_promotion:
+  ; CHECK: movzbl ({{.*}})
+  %arrayidx = getelementptr inbounds i8* %0, i8 %add
+
+  %1 = load i8* %arrayidx, align 1
+  ret i8 %1
+}
+
+define zeroext i8 @gep_promotion_nonconst(i8 %i, i8* %ptr) nounwind uwtable ssp {
+entry:
+  %i.addr = alloca i8, align 4
+  %ptr.addr = alloca i8*, align 8
+  store i8 %i, i8* %i.addr, align 4
+  store i8* %ptr, i8** %ptr.addr, align 8
+  %0 = load i8* %i.addr, align 4
+  ; CHECK-LABEL: _gep_promotion_nonconst:
+  ; CHECK: movzbl ({{.*}})
+  %xor = xor i8 %0, -128   ; %0   ^ 0x80
+  %add = add i8 %xor, -127 ; %xor + 0x81
+  %1 = load i8** %ptr.addr, align 8
+
+  %arrayidx = getelementptr inbounds i8* %1, i8 %add
+
+  %2 = load i8* %arrayidx, align 1
+  ret i8 %2
+}
+