Model sqrtss as a binary operation with one source operand tied to the destination (PR14221)

[spatel]

Summary

This is a continuation of r167064 ( http://llvm.org/viewvc/llvm-project?view=revision&revision=167064 ).
That patch started to fix PR14221 ( http://llvm.org/bugs/show_bug.cgi?id=14221 ), but was not completed, so we have a chunk of extra code that is preventing further improvements.

If everything looks ok here, I can submit a follow-on patch to fix sqrtsd (double-precision square root).

I'm not locating a Phab address for Manman Ren, so I'll send a follow-on mail.

[spatel]

Ping.

[spatel]

Ping * 2.

...we are miscompiling code without this patch as shown in http://llvm.org/bugs/show_bug.cgi?id=14221 .

[spatel]

Ping * 3.

[RKSimon]

Is there anything stopping the sse1_fp_unop_* and sse2_fp_unop_* defs being merged into sse12_fp_unop_* like the binops already have been? SQRTSD is the only reference to sse2_fp_unop_s and generally there is a high level of code duplication between the 2 sets of defs that the sse12_ types reduce a lot.

[spatel]

In D6330#101289, @RKSimon wrote:

Is there anything stopping the sse1_fp_unop_* and sse2_fp_unop_* defs being merged into sse12_fp_unop_* like the binops already have been? SQRTSD is the only reference to sse2_fp_unop_s and generally there is a high level of code duplication between the 2 sets of defs that the sse12_ types reduce a lot.

I was planning to fix sqrtsd in a follow-on patch. I agree that there's more consolidation possible, and I don't think there's anything that would prevent handling the unop cases similarly to the binop cases.

[spatel]

Ping * 4.

[delena]

I checked this patch and it LGTM.

• Elena

[hliao]

LGTM. Sorry for the really LATE reply.

[spatel]

Thanks, Elena and Michael! Checked in with r224624.

lib/Target/X86/X86InstrSSE.td

def SSE_RCPP : OpndItins<
   IIC_SSE_RCPP_RR, IIC_SSE_RCPP_RM
 >;
 
 def SSE_RCPS : OpndItins<
   IIC_SSE_RCPS_RR, IIC_SSE_RCPS_RM
 >;
 }
 
-/// sse1_fp_unop_s - SSE1 unops in scalar form.
-multiclass sse1_fp_unop_s<bits<8> opc, string OpcodeStr,
-                          SDNode OpNode, Intrinsic F32Int, OpndItins itins> {
-let Predicates = [HasAVX], hasSideEffects = 0 in {
-  def V#NAME#SSr : SSI<opc, MRMSrcReg, (outs FR32:$dst),
-                      (ins FR32:$src1, FR32:$src2),
-                      !strconcat("v", OpcodeStr,
-                                 "ss\t{$src2, $src1, $dst|$dst, $src1, $src2}"),
-                      []>, VEX_4V, VEX_LIG, Sched<[itins.Sched]>;
-  let mayLoad = 1 in {
-  def V#NAME#SSm : SSI<opc, MRMSrcMem, (outs FR32:$dst),
-                      (ins FR32:$src1,f32mem:$src2),
-                      !strconcat("v", OpcodeStr,
-                                 "ss\t{$src2, $src1, $dst|$dst, $src1, $src2}"),
-                      []>, VEX_4V, VEX_LIG,
-                   Sched<[itins.Sched.Folded, ReadAfterLd]>;
-  let isCodeGenOnly = 1 in
-  def V#NAME#SSm_Int : SSI<opc, MRMSrcMem, (outs VR128:$dst),
-                      (ins VR128:$src1, ssmem:$src2),
-                      !strconcat("v", OpcodeStr,
-                                 "ss\t{$src2, $src1, $dst|$dst, $src1, $src2}"),
-                      []>, VEX_4V, VEX_LIG,
-                      Sched<[itins.Sched.Folded, ReadAfterLd]>;
-  }
-}
-
-  def SSr : SSI<opc, MRMSrcReg, (outs FR32:$dst), (ins FR32:$src),
-                !strconcat(OpcodeStr, "ss\t{$src, $dst|$dst, $src}"),
-                [(set FR32:$dst, (OpNode FR32:$src))]>, Sched<[itins.Sched]>;
-  // For scalar unary operations, fold a load into the operation
-  // only in OptForSize mode. It eliminates an instruction, but it also
-  // eliminates a whole-register clobber (the load), so it introduces a
-  // partial register update condition.
-  def SSm : I<opc, MRMSrcMem, (outs FR32:$dst), (ins f32mem:$src),
-                !strconcat(OpcodeStr, "ss\t{$src, $dst|$dst, $src}"),
-                [(set FR32:$dst, (OpNode (load addr:$src)))], itins.rm>, XS,
-            Requires<[UseSSE1, OptForSize]>, Sched<[itins.Sched.Folded]>;
-let isCodeGenOnly = 1 in {
-  def SSr_Int : SSI<opc, MRMSrcReg, (outs VR128:$dst), (ins VR128:$src),
-                    !strconcat(OpcodeStr, "ss\t{$src, $dst|$dst, $src}"),
-                    [(set VR128:$dst, (F32Int VR128:$src))], itins.rr>,
-                Sched<[itins.Sched]>;
-  def SSm_Int : SSI<opc, MRMSrcMem, (outs VR128:$dst), (ins ssmem:$src),
-                    !strconcat(OpcodeStr, "ss\t{$src, $dst|$dst, $src}"),
-                    [(set VR128:$dst, (F32Int sse_load_f32:$src))], itins.rm>,
-                Sched<[itins.Sched.Folded]>;
-}
-}
-
-/// sse1_fp_unop_s_rw - SSE1 unops where vector form has a read-write operand.
-multiclass sse1_fp_unop_rw<bits<8> opc, string OpcodeStr, SDNode OpNode,
+/// sse1_fp_unop_s - SSE1 unops in scalar form
+/// For the non-AVX defs, we need $src1 to be tied to $dst because
+/// the HW instructions are 2 operand / destructive.
+multiclass sse1_fp_unop_s<bits<8> opc, string OpcodeStr, SDNode OpNode,
                            OpndItins itins> {
 let Predicates = [HasAVX], hasSideEffects = 0 in {
   def V#NAME#SSr : SSI<opc, MRMSrcReg, (outs FR32:$dst),
                        (ins FR32:$src1, FR32:$src2),
                        !strconcat("v", OpcodeStr,
                            "ss\t{$src2, $src1, $dst|$dst, $src1, $src2}"),
                 []>, VEX_4V, VEX_LIG, Sched<[itins.Sched]>;
   let mayLoad = 1 in {
def PDr : PDI<opc, MRMSrcReg, (outs VR128:$dst), (ins VR128:$src),
             Sched<[itins.Sched]>;
   def PDm : PDI<opc, MRMSrcMem, (outs VR128:$dst), (ins f128mem:$src),
                 !strconcat(OpcodeStr, "pd\t{$src, $dst|$dst, $src}"),
                 [(set VR128:$dst, (OpNode (memopv2f64 addr:$src)))], itins.rm>,
             Sched<[itins.Sched.Folded]>;
 }
 
 // Square root.
-defm SQRT  : sse1_fp_unop_s<0x51, "sqrt",  fsqrt, int_x86_sse_sqrt_ss,
-                            SSE_SQRTSS>,
+defm SQRT  : sse1_fp_unop_s<0x51, "sqrt", fsqrt, SSE_SQRTSS>,
              sse1_fp_unop_p<0x51, "sqrt", fsqrt, SSE_SQRTPS>,
-             sse2_fp_unop_s<0x51, "sqrt",  fsqrt, int_x86_sse2_sqrt_sd,
+             sse2_fp_unop_s<0x51, "sqrt", fsqrt, int_x86_sse2_sqrt_sd,
                             SSE_SQRTSD>,
              sse2_fp_unop_p<0x51, "sqrt", fsqrt, SSE_SQRTPD>;
 
 // Reciprocal approximations. Note that these typically require refinement
 // in order to obtain suitable precision.
-defm RSQRT : sse1_fp_unop_rw<0x52, "rsqrt", X86frsqrt, SSE_RSQRTSS>,
+defm RSQRT : sse1_fp_unop_s<0x52, "rsqrt", X86frsqrt, SSE_RSQRTSS>,
              sse1_fp_unop_p<0x52, "rsqrt", X86frsqrt, SSE_RSQRTPS>,
              sse1_fp_unop_p_int<0x52, "rsqrt", int_x86_sse_rsqrt_ps,
                                 int_x86_avx_rsqrt_ps_256, SSE_RSQRTPS>;
-defm RCP   : sse1_fp_unop_rw<0x53, "rcp", X86frcp, SSE_RCPS>,
+defm RCP   : sse1_fp_unop_s<0x53, "rcp", X86frcp, SSE_RCPS>,
              sse1_fp_unop_p<0x53, "rcp", X86frcp, SSE_RCPP>,
              sse1_fp_unop_p_int<0x53, "rcp", int_x86_sse_rcp_ps,
                                 int_x86_avx_rcp_ps_256, SSE_RCPP>;
 
 let Predicates = [UseAVX] in {
   def : Pat<(f32 (fsqrt FR32:$src)),
             (VSQRTSSr (f32 (IMPLICIT_DEF)), FR32:$src)>, Requires<[HasAVX]>;
   def : Pat<(f32 (fsqrt (load addr:$src))),
let Predicates = [HasAVX] in {
   def : Pat<(int_x86_sse_rcp_ss VR128:$src),
             (COPY_TO_REGCLASS (VRCPSSr (f32 (IMPLICIT_DEF)),
                                        (COPY_TO_REGCLASS VR128:$src, FR32)),
                               VR128)>;
   def : Pat<(int_x86_sse_rcp_ss sse_load_f32:$src),
             (VRCPSSm_Int (v4f32 (IMPLICIT_DEF)), sse_load_f32:$src)>;
 }
 
-// Reciprocal approximations. Note that these typically require refinement
-// in order to obtain suitable precision.
+// These are unary operations, but they are modeled as having 2 source operands
+// to match the AVX defs (the high elements of the destination are unchanged in
+// SSE).
 let Predicates = [UseSSE1] in {
   def : Pat<(int_x86_sse_rsqrt_ss VR128:$src),
             (RSQRTSSr_Int VR128:$src, VR128:$src)>;
   def : Pat<(int_x86_sse_rcp_ss VR128:$src),
             (RCPSSr_Int VR128:$src, VR128:$src)>;
+  def : Pat<(int_x86_sse_sqrt_ss VR128:$src),
+            (SQRTSSr_Int VR128:$src, VR128:$src)>;
 }
 
 // There is no f64 version of the reciprocal approximation instructions.
 
 //===----------------------------------------------------------------------===//
 // SSE 1 & 2 - Non-temporal stores
 //===----------------------------------------------------------------------===//
 

test/CodeGen/X86/sse_partial_update.ll

; CHECK: rcpss %xmm0, %xmm0
   %a.addr.0.extract = extractelement <4 x float> %0, i32 0
   %conv = fpext float %a.addr.0.extract to double
   %a.addr.4.extract = extractelement <4 x float> %0, i32 1
   %conv3 = fpext float %a.addr.4.extract to double
   tail call void @callee(double %conv, double %conv3) nounwind
   ret void
 }
 declare <4 x float> @llvm.x86.sse.rcp.ss(<4 x float>) nounwind readnone
+
+define void @sqrtss(<4 x float> %a) nounwind uwtable ssp {
+entry:
+; CHECK-LABEL: sqrtss:
+; CHECK: sqrtss %xmm0, %xmm0
+  %0 = tail call <4 x float> @llvm.x86.sse.sqrt.ss(<4 x float> %a) nounwind
+  %a.addr.0.extract = extractelement <4 x float> %0, i32 0
+  %conv = fpext float %a.addr.0.extract to double
+  %a.addr.4.extract = extractelement <4 x float> %0, i32 1
+  %conv3 = fpext float %a.addr.4.extract to double
+  tail call void @callee(double %conv, double %conv3) nounwind
+  ret void
+}
+declare <4 x float> @llvm.x86.sse.sqrt.ss(<4 x float>) nounwind readnone