Fix lowering ARM shift by zero as a move.

ARM does not support shifting by 0. An immediate value of 0 is interpreted as shifting by 32. See section A8.4.1 Constant shifts of the ARMv7-A/R reference manual. Change-Id: I289a7c6091c04387700dc2e9b3f959639bd919ce Reviewed-on: https://chromium-review.googlesource.com/491949Reviewed-by: Jim Stichnoth <stichnot@chromium.org>

Fix lowering ARM shift by zero as a move.
fb705a6d · Nicolas Capens · Nicolas Capens · 6c629dc3 · fb705a6d
Commit fb705a6d authored May 01, 2017 by Nicolas Capens Committed by Nicolas Capens May 02, 2017
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Showing with 24 additions and 5 deletions

IceTargetLoweringARM32.cpp src/IceTargetLoweringARM32.cpp +24 -5

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--- a/src/IceTargetLoweringARM32.cpp
+++ b/src/IceTargetLoweringARM32.cpp
@@ -2513,6 +2513,13 @@ public:
    return legalizeToReg(Target, Swapped ? Src0 : Src1);
  }

+  bool isSrc1ImmediateZero() const {
+    if (!swappedOperands() && hasConstOperand()) {
+      return getConstantValue() == 0;
+    }
+    return false;
+  }
+
  bool immediateIsFlexEncodable() const {
    uint32_t Rotate, Imm8;
    return OperandARM32FlexImm::canHoldImm(getConstantValue(), &Rotate, &Imm8);
@@ -3422,8 +3429,12 @@ void TargetARM32::lowerArithmetic(const InstArithmetic *Instr) {
  case InstArithmetic::Shl: {
    Variable *Src0R = Srcs.unswappedSrc0R(this);
    if (!isVectorType(T->getType())) {
-      Operand *Src1R = Srcs.unswappedSrc1RShAmtImm(this);
-      _lsl(T, Src0R, Src1R);
+      if (Srcs.isSrc1ImmediateZero()) {
+        _mov(T, Src0R);
+      } else {
+        Operand *Src1R = Srcs.unswappedSrc1RShAmtImm(this);
+        _lsl(T, Src0R, Src1R);
+      }
    } else {
      auto *Src1R = Srcs.unswappedSrc1R(this);
      _vshl(T, Src0R, Src1R)->setSignType(InstARM32::FS_Unsigned);
@@ -3434,11 +3445,15 @@ void TargetARM32::lowerArithmetic(const InstArithmetic *Instr) {
  case InstArithmetic::Lshr: {
    Variable *Src0R = Srcs.unswappedSrc0R(this);
    if (!isVectorType(T->getType())) {
-      Operand *Src1R = Srcs.unswappedSrc1RShAmtImm(this);
      if (DestTy != IceType_i32) {
        _uxt(Src0R, Src0R);
      }
-      _lsr(T, Src0R, Src1R);
+      if (Srcs.isSrc1ImmediateZero()) {
+        _mov(T, Src0R);
+      } else {
+        Operand *Src1R = Srcs.unswappedSrc1RShAmtImm(this);
+        _lsr(T, Src0R, Src1R);
+      }
    } else {
      auto *Src1R = Srcs.unswappedSrc1R(this);
      auto *Src1RNeg = makeReg(Src1R->getType());
@@ -3454,7 +3469,11 @@ void TargetARM32::lowerArithmetic(const InstArithmetic *Instr) {
      if (DestTy != IceType_i32) {
        _sxt(Src0R, Src0R);
      }
-      _asr(T, Src0R, Srcs.unswappedSrc1RShAmtImm(this));
+      if (Srcs.isSrc1ImmediateZero()) {
+        _mov(T, Src0R);
+      } else {
+        _asr(T, Src0R, Srcs.unswappedSrc1RShAmtImm(this));
+      }
    } else {
      auto *Src1R = Srcs.unswappedSrc1R(this);
      auto *Src1RNeg = makeReg(Src1R->getType());