Subzero: Improve lowering sequence for "a=b*b".

tests_lit/llvm2ice_tests/square.ll

+; Test the a=b*b lowering sequence which can use a single temporary register
+; instead of two registers.
+
+; RUN: %if --need=target_X8632 --command %p2i --filetype=obj --disassemble \
+; RUN:   --target x8632 -i %s --args -O2 -mattr=sse4.1 \
+; RUN:   | %if --need=target_X8632 --command FileCheck %s
+
+; RUN: %if --need=target_X8632 --command %p2i --filetype=obj --disassemble \
+; RUN:   --target x8632 -i %s --args -Om1 -mattr=sse4.1 \
+; RUN:   | %if --need=target_X8632 --command FileCheck %s
+
+define float @Square_float(float %a) {
+entry:
+  %result = fmul float %a, %a
+  ret float %result
+}
+; CHECK-LABEL: Square_float
+; CHECK: mulss [[REG:xmm.]],[[REG]]
+
+define double @Square_double(double %a) {
+entry:
+  %result = fmul double %a, %a
+  ret double %result
+}
+; CHECK-LABEL: Square_double
+; CHECK: mulsd [[REG:xmm.]],[[REG]]
+
+define i32 @Square_i32(i32 %a) {
+entry:
+  %result = mul i32 %a, %a
+  ret i32 %result
+}
+; CHECK-LABEL: Square_i32
+; CHECK: imul [[REG:e..]],[[REG]]
+
+define i16 @Square_i16(i16 %a) {
+entry:
+  %result = mul i16 %a, %a
+  ret i16 %result
+}
+; CHECK-LABEL: Square_i16
+; CHECK: imul [[REG:..]],[[REG]]
+
+define i8 @Square_i8(i8 %a) {
+entry:
+  %result = mul i8 %a, %a
+  ret i8 %result
+}
+; CHECK-LABEL: Square_i8
+; CHECK: imul al
+
+define <4 x float> @Square_v4f32(<4 x float> %a) {
+entry:
+  %result = fmul <4 x float> %a, %a
+  ret <4 x float> %result
+}
+; CHECK-LABEL: Square_v4f32
+; CHECK: mulps [[REG:xmm.]],[[REG]]
+
+define <4 x i32> @Square_v4i32(<4 x i32> %a) {
+entry:
+  %result = mul <4 x i32> %a, %a
+  ret <4 x i32> %result
+}
+; CHECK-LABEL: Square_v4i32
+; CHECK: pmulld [[REG:xmm.]],[[REG]]
+
+define <8 x i16> @Square_v8i16(<8 x i16> %a) {
+entry:
+  %result = mul <8 x i16> %a, %a
+  ret <8 x i16> %result
+}
+; CHECK-LABEL: Square_v8i16
+; CHECK: pmullw [[REG:xmm.]],[[REG]]
+
+define <16 x i8> @Square_v16i8(<16 x i8> %a) {
+entry:
+  %result = mul <16 x i8> %a, %a
+  ret <16 x i8> %result
+}
+; CHECK-LABEL: Square_v16i8
+; CHECK-NOT: pmul