Subzero: Generate correct code for shifts by a large immediate.

src/IceAssemblerX86BaseImpl.h

@@ -3371,7 +3371,10 @@ template <class Machine>
 void AssemblerX86Base<Machine>::emitGenericShift(
     int rm, Type Ty, typename Traits::GPRRegister reg, const Immediate &imm) {
   AssemblerBuffer::EnsureCapacity ensured(&Buffer);
-  assert(imm.is_int8());
+  // We don't assert that imm fits into 8 bits; instead, it gets masked below.
+  // Note that we don't mask it further (e.g. to 5 bits) because we want the
+  // same processor behavior regardless of whether it's an immediate (masked to
+  // 8 bits) or in register cl (essentially ecx masked to 8 bits).
   if (Ty == IceType_i16)
     emitOperandSizeOverride();
   emitRexB(Ty, reg);

tests_lit/llvm2ice_tests/shift.ll

@@ -64,3 +64,51 @@ entry:
 ; ARM32-LABEL: conv2
 ; ARM32: lsl {{.*}}, #16
 ; ARM32: lsr {{.*}}, #16
+
+define i32 @shlImmLarge(i32 %val) {
+entry:
+  %result = shl i32 %val, 257
+  ret i32 %result
+}
+; CHECK-LABEL: shlImmLarge
+; CHECK: shl {{.*}},0x1
+
+define i32 @shlImmNeg(i32 %val) {
+entry:
+  %result = shl i32 %val, -1
+  ret i32 %result
+}
+; CHECK-LABEL: shlImmNeg
+; CHECK: shl {{.*}},0xff
+
+define i32 @lshrImmLarge(i32 %val) {
+entry:
+  %result = lshr i32 %val, 257
+  ret i32 %result
+}
+; CHECK-LABEL: lshrImmLarge
+; CHECK: shr {{.*}},0x1
+
+define i32 @lshrImmNeg(i32 %val) {
+entry:
+  %result = lshr i32 %val, -1
+  ret i32 %result
+}
+; CHECK-LABEL: lshrImmNeg
+; CHECK: shr {{.*}},0xff
+
+define i32 @ashrImmLarge(i32 %val) {
+entry:
+  %result = ashr i32 %val, 257
+  ret i32 %result
+}
+; CHECK-LABEL: ashrImmLarge
+; CHECK: sar {{.*}},0x1
+
+define i32 @ashrImmNeg(i32 %val) {
+entry:
+  %result = ashr i32 %val, -1
+  ret i32 %result
+}
+; CHECK-LABEL: ashrImmNeg
+; CHECK: sar {{.*}},0xff