ARM assembler: fix undefined behaviour in fits_shifter

src/arm/assembler-arm.cc

Index: src/arm/assembler-arm.cc
diff --git a/src/arm/assembler-arm.cc b/src/arm/assembler-arm.cc
index 7a091d0deb354d6a8b68b14041de82ae4df08e3f..2bf48e58dc3c9db8ff7b1da910590ecd3ddf3388 100644
--- a/src/arm/assembler-arm.cc
+++ b/src/arm/assembler-arm.cc
@@ -1011,7 +1011,8 @@ static bool fits_shifter(uint32_t imm32,
                          Instr* instr) {
   // imm32 must be unsigned.
   for (int rot = 0; rot < 16; rot++) {
-    uint32_t imm8 = (imm32 << 2*rot) | (imm32 >> (32 - 2*rot));
+    uint32_t imm8 =
+        rot == 0 ? imm32 : (imm32 << 2 * rot) | (imm32 >> (32 - 2 * rot));
     if ((imm8 <= 0xff)) {
       *rotate_imm = rot;
       *immed_8 = imm8;