[x86] increment/decrement constant vector with min/max in vsetcc lowering (PR39859)

[spatel]

Summary

This is part of fixing PR39859:
https://bugs.llvm.org/show_bug.cgi?id=39859

We have a crippled vector ISA, so we have to invert a typical fold and create min/max here.

As discussed in the bug report, we can probably do better by using saturating subtract in larger patterns when it's available, but we should have this improvement for the minimal patterns regardless.

Alive proofs:
https://rise4fun.com/Alive/zsf
https://rise4fun.com/Alive/Qrl

[RKSimon]

lib/Target/X86/X86ISelLowering.cpp

19394

Can you use ISD::matchUnaryPredicate and get this TODO done straightaway?

[spatel]

lib/Target/X86/X86ISelLowering.cpp

19394

I didn't think about using matchUnaryPredicate, but that is a possibility. We have this already:
rL348776
I was planning to generalize that (doesn't seem to handle undef elements either) and lift it out of x86. We have things like that in InstCombine called "AddOne" and "SubOne".

But I think it's best to make it a follow-up either way to avoid bug risk in that conversion.

[nikic]

Are there any tests for the 0/max cases? (I guess they're probably just constant folded away anyway?)

[spatel]

In D55515#1326183, @nikic wrote:

Are there any tests for the 0/max cases? (I guess they're probably just constant folded away anyway?)

No - I can add those, but it's probably hard to get that pattern this deep into SDAG.
And yes, we would hope that those would always get folded, but nothing is certain in SDAG which is why I could not just assert that those cases are impossible.

[spatel]

Patch updated:
Add tests for vsetcc simplification edge cases. These are currently folded early in generic DAGCombiner via SimplifySetCC().

[RKSimon]

LGTM - hope to see the non-splat vector support soon.

lib/Target/X86/X86ISelLowering.cpp

#endif
 
   // If both operands are known non-negative, then an unsigned compare is the
   // same as a signed compare and there's no need to flip signbits.
   // TODO: We could check for more general simplifications here since we're
   // computing known bits.
   bool FlipSigns = ISD::isUnsignedIntSetCC(Cond) &&
                    !(DAG.SignBitIsZero(Op0) && DAG.SignBitIsZero(Op1));
 
-  // Special case: Use min/max operations for unsigned compares. We only want
-  // to do this for unsigned compares if we need to flip signs or if it allows
-  // use to avoid an invert.
+  // Special case: Use min/max operations for unsigned compares.
   const TargetLowering &TLI = DAG.getTargetLoweringInfo();
   if (ISD::isUnsignedIntSetCC(Cond) &&
       (FlipSigns || ISD::isTrueWhenEqual(Cond)) &&
       TLI.isOperationLegal(ISD::UMIN, VT)) {
+    // If we have a constant operand, increment/decrement it and change the
+    // condition to avoid an invert.
+    // TODO: This could be extended to handle a non-splat constant by checking
+    // that each element of the constant is not the max/null value.
+    APInt C;
+    if (Cond == ISD::SETUGT && isConstantSplat(Op1, C) && !C.isMaxValue()) {
+      // X > C --> X >= (C+1) --> X == umax(X, C+1)
+      Op1 = DAG.getConstant(C + 1, dl, VT);
+      Cond = ISD::SETUGE;
+    }
+    if (Cond == ISD::SETULT && isConstantSplat(Op1, C) && !C.isNullValue()) {
+      // X < C --> X <= (C-1) --> X == umin(X, C-1)
+      Op1 = DAG.getConstant(C - 1, dl, VT);
+      Cond = ISD::SETULE;
+    }
     bool Invert = false;
     unsigned Opc;
     switch (Cond) {
     default: llvm_unreachable("Unexpected condition code");
     case ISD::SETUGT: Invert = true; LLVM_FALLTHROUGH;
     case ISD::SETULE: Opc = ISD::UMIN; break;
     case ISD::SETULT: Invert = true; LLVM_FALLTHROUGH;
     case ISD::SETUGE: Opc = ISD::UMAX; break;

test/CodeGen/X86/sat-add.ll

 ; SSE2-NEXT:    pcmpgtd {{.*}}(%rip), %xmm0
 ; SSE2-NEXT:    por %xmm1, %xmm0
 ; SSE2-NEXT:    retq
 ;
 ; SSE41-LABEL: unsigned_sat_constant_v4i32_using_cmp_notval:
 ; SSE41:       # %bb.0:
 ; SSE41-NEXT:    movdqa {{.*#+}} xmm1 = [42,42,42,42]
 ; SSE41-NEXT:    paddd %xmm0, %xmm1
-; SSE41-NEXT:    movdqa {{.*#+}} xmm2 = [4294967253,4294967253,4294967253,4294967253]
-; SSE41-NEXT:    pminud %xmm0, %xmm2
+; SSE41-NEXT:    movdqa {{.*#+}} xmm2 = [4294967254,4294967254,4294967254,4294967254]
+; SSE41-NEXT:    pmaxud %xmm0, %xmm2
 ; SSE41-NEXT:    pcmpeqd %xmm2, %xmm0
-; SSE41-NEXT:    pcmpeqd %xmm2, %xmm2
-; SSE41-NEXT:    pxor %xmm2, %xmm0
 ; SSE41-NEXT:    por %xmm1, %xmm0
 ; SSE41-NEXT:    retq
   %a = add <4 x i32> %x, <i32 42, i32 42, i32 42, i32 42>
   %c = icmp ugt <4 x i32> %x, <i32 -43, i32 -43, i32 -43, i32 -43>
   %r = select <4 x i1> %c, <4 x i32> <i32 -1, i32 -1, i32 -1, i32 -1>, <4 x i32> %a
   ret <4 x i32> %r
 }
 

test/CodeGen/X86/vec_minmax_match.ll

; CHECK-NEXT:    retq
   %r = select <4 x i1> %cmp1, <4 x i32><i32 255, i32 255, i32 255, i32 255>, <4 x i32> %max
   ret <4 x i32> %r
 }
 
 define <4 x i32> @wrong_pred_for_smin_with_not(<4 x i32> %x) {
 ; CHECK-LABEL: wrong_pred_for_smin_with_not:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    vpcmpeqd %xmm1, %xmm1, %xmm1
-; CHECK-NEXT:    vpxor %xmm1, %xmm0, %xmm2
-; CHECK-NEXT:    vpminud {{.*}}(%rip), %xmm0, %xmm3
-; CHECK-NEXT:    vpcmpeqd %xmm3, %xmm0, %xmm0
-; CHECK-NEXT:    vpxor %xmm1, %xmm0, %xmm0
-; CHECK-NEXT:    vmovaps {{.*#+}} xmm1 = [4294967291,4294967291,4294967291,4294967291]
-; CHECK-NEXT:    vblendvps %xmm0, %xmm2, %xmm1, %xmm0
+; CHECK-NEXT:    vpxor %xmm1, %xmm0, %xmm1
+; CHECK-NEXT:    vpmaxud {{.*}}(%rip), %xmm0, %xmm2
+; CHECK-NEXT:    vpcmpeqd %xmm2, %xmm0, %xmm0
+; CHECK-NEXT:    vmovaps {{.*#+}} xmm2 = [4294967291,4294967291,4294967291,4294967291]
+; CHECK-NEXT:    vblendvps %xmm0, %xmm1, %xmm2, %xmm0
 ; CHECK-NEXT:    retq
   %not_x = xor <4 x i32> %x, <i32 -1, i32 -1, i32 -1, i32 -1>
   %cmp = icmp ugt <4 x i32> %x, <i32 4, i32 4, i32 4, i32 4>
   %sel = select <4 x i1> %cmp, <4 x i32> %not_x, <4 x i32> <i32 -5, i32 -5, i32 -5, i32 -5>
   ret <4 x i32> %sel
 }
 
 define <4 x i32> @wrong_pred_for_smin_with_subnsw(<4 x i32> %x, <4 x i32> %y) {

test/CodeGen/X86/vec_setcc-2.ll

 ; SSE2-NEXT:    retq
 ;
 ; SSE41-LABEL: loop_no_const_reload:
 ; SSE41:       ## %bb.0: ## %entry
 ; SSE41-NEXT:    testl %edx, %edx
 ; SSE41-NEXT:    je LBB0_3
 ; SSE41-NEXT:  ## %bb.1: ## %for.body.preheader
 ; SSE41-NEXT:    xorl %eax, %eax
-; SSE41-NEXT:    movdqa {{.*#+}} xmm0 = [26,26,26,26,26,26,26,26]
-; SSE41-NEXT:    pcmpeqd %xmm1, %xmm1
+; SSE41-NEXT:    movdqa {{.*#+}} xmm0 = [25,25,25,25,25,25,25,25]
 ; SSE41-NEXT:    .p2align 4, 0x90
 ; SSE41-NEXT:  LBB0_2: ## %for.body
 ; SSE41-NEXT:    ## =>This Inner Loop Header: Depth=1
-; SSE41-NEXT:    movdqa (%rdi,%rax), %xmm2
-; SSE41-NEXT:    movdqa %xmm2, %xmm3
-; SSE41-NEXT:    pmaxuw %xmm0, %xmm3
-; SSE41-NEXT:    pcmpeqw %xmm2, %xmm3
-; SSE41-NEXT:    pxor %xmm1, %xmm3
-; SSE41-NEXT:    movdqa %xmm3, (%rsi,%rax)
+; SSE41-NEXT:    movdqa (%rdi,%rax), %xmm1
+; SSE41-NEXT:    movdqa %xmm1, %xmm2
+; SSE41-NEXT:    pminuw %xmm0, %xmm2
+; SSE41-NEXT:    pcmpeqw %xmm1, %xmm2
+; SSE41-NEXT:    movdqa %xmm2, (%rsi,%rax)
 ; SSE41-NEXT:    addq $16, %rax
 ; SSE41-NEXT:    decl %edx
 ; SSE41-NEXT:    jne LBB0_2
 ; SSE41-NEXT:  LBB0_3: ## %for.end
 ; SSE41-NEXT:    retq
 entry:
   %cmp9 = icmp eq i32 %n, 0
   br i1 %cmp9, label %for.end, label %for.body
for.end:                                          ; preds = %for.body, %entry
   ret void
 }
 
 ; Test for PSUBUSB
 
 define <16 x i8> @test_ult_byte(<16 x i8> %a) {
 ; CHECK-LABEL: test_ult_byte:
 ; CHECK:       ## %bb.0: ## %entry
-; CHECK-NEXT:    movdqa {{.*#+}} xmm1 = [11,11,11,11,11,11,11,11,11,11,11,11,11,11,11,11]
-; CHECK-NEXT:    pmaxub %xmm0, %xmm1
+; CHECK-NEXT:    movdqa {{.*#+}} xmm1 = [10,10,10,10,10,10,10,10,10,10,10,10,10,10,10,10]
+; CHECK-NEXT:    pminub %xmm0, %xmm1
 ; CHECK-NEXT:    pcmpeqb %xmm1, %xmm0
-; CHECK-NEXT:    pcmpeqd %xmm1, %xmm1
-; CHECK-NEXT:    pxor %xmm1, %xmm0
 ; CHECK-NEXT:    retq
 entry:
   %icmp = icmp ult <16 x i8> %a, <i8 11, i8 11, i8 11, i8 11, i8 11, i8 11, i8 11, i8 11, i8 11, i8 11, i8 11, i8 11, i8 11, i8 11, i8 11, i8 11>
   %sext = sext <16 x i1> %icmp to <16 x i8>
   ret <16 x i8> %sext
 }
 
 ; Only do this when we can turn the comparison into a setule.  I.e. not for
entry:
   %icmp = icmp ult <8 x i16> %a, %b
   %sext = sext <8 x i1> %icmp to <8 x i16>
   ret <8 x i16> %sext
 }
 
 define <16 x i1> @ugt_v16i8_splat(<16 x i8> %x) {
 ; CHECK-LABEL: ugt_v16i8_splat:
 ; CHECK:       ## %bb.0:
-; CHECK-NEXT:    movdqa {{.*#+}} xmm1 = [42,42,42,42,42,42,42,42,42,42,42,42,42,42,42,42]
-; CHECK-NEXT:    pminub %xmm0, %xmm1
+; CHECK-NEXT:    movdqa {{.*#+}} xmm1 = [43,43,43,43,43,43,43,43,43,43,43,43,43,43,43,43]
+; CHECK-NEXT:    pmaxub %xmm0, %xmm1
 ; CHECK-NEXT:    pcmpeqb %xmm1, %xmm0
-; CHECK-NEXT:    pcmpeqd %xmm1, %xmm1
-; CHECK-NEXT:    pxor %xmm1, %xmm0
 ; CHECK-NEXT:    retq
   %cmp = icmp ugt <16 x i8> %x, <i8 42, i8 42, i8 42, i8 42, i8 42, i8 42, i8 42, i8 42, i8 42, i8 42, i8 42, i8 42, i8 42, i8 42, i8 42, i8 42>
   ret <16 x i1> %cmp
 }
 
 define <8 x i1> @ugt_v8i16_splat(<8 x i16> %x) {
 ; SSE2-LABEL: ugt_v8i16_splat:
 ; SSE2:       ## %bb.0:
 ; SSE2-NEXT:    pxor {{.*}}(%rip), %xmm0
 ; SSE2-NEXT:    pcmpgtw {{.*}}(%rip), %xmm0
 ; SSE2-NEXT:    retq
 ;
 ; SSE41-LABEL: ugt_v8i16_splat:
 ; SSE41:       ## %bb.0:
-; SSE41-NEXT:    movdqa {{.*#+}} xmm1 = [242,242,242,242,242,242,242,242]
-; SSE41-NEXT:    pminuw %xmm0, %xmm1
+; SSE41-NEXT:    movdqa {{.*#+}} xmm1 = [243,243,243,243,243,243,243,243]
+; SSE41-NEXT:    pmaxuw %xmm0, %xmm1
 ; SSE41-NEXT:    pcmpeqw %xmm1, %xmm0
-; SSE41-NEXT:    pcmpeqd %xmm1, %xmm1
-; SSE41-NEXT:    pxor %xmm1, %xmm0
 ; SSE41-NEXT:    retq
   %cmp = icmp ugt <8 x i16> %x, <i16 242, i16 242, i16 242, i16 242, i16 242, i16 242, i16 242, i16 242>
   ret <8 x i1> %cmp
 }
 
 define <4 x i1> @ugt_v4i32_splat(<4 x i32> %x) {
 ; SSE2-LABEL: ugt_v4i32_splat:
 ; SSE2:       ## %bb.0:
 ; SSE2-NEXT:    pxor {{.*}}(%rip), %xmm0
 ; SSE2-NEXT:    pcmpgtd {{.*}}(%rip), %xmm0
 ; SSE2-NEXT:    retq
 ;
 ; SSE41-LABEL: ugt_v4i32_splat:
 ; SSE41:       ## %bb.0:
-; SSE41-NEXT:    movdqa {{.*#+}} xmm1 = [4294967254,4294967254,4294967254,4294967254]
-; SSE41-NEXT:    pminud %xmm0, %xmm1
+; SSE41-NEXT:    movdqa {{.*#+}} xmm1 = [4294967255,4294967255,4294967255,4294967255]
+; SSE41-NEXT:    pmaxud %xmm0, %xmm1
 ; SSE41-NEXT:    pcmpeqd %xmm1, %xmm0
-; SSE41-NEXT:    pcmpeqd %xmm1, %xmm1
-; SSE41-NEXT:    pxor %xmm1, %xmm0
 ; SSE41-NEXT:    retq
   %cmp = icmp ugt <4 x i32> %x, <i32 -42, i32 -42, i32 -42, i32 -42>
   ret <4 x i1> %cmp
 }
 
 define <2 x i1> @ugt_v2i64_splat(<2 x i64> %x) {
 ; SSE2-LABEL: ugt_v2i64_splat:
 ; SSE2:       ## %bb.0:

 ; SSE41-NEXT:    retq
   %cmp = icmp uge <2 x i64> %x, <i64 442, i64 442>
   ret <2 x i1> %cmp
 }
 
 define <16 x i1> @ult_v16i8_splat(<16 x i8> %x) {
 ; CHECK-LABEL: ult_v16i8_splat:
 ; CHECK:       ## %bb.0:
-; CHECK-NEXT:    movdqa {{.*#+}} xmm1 = [42,42,42,42,42,42,42,42,42,42,42,42,42,42,42,42]
-; CHECK-NEXT:    pmaxub %xmm0, %xmm1
+; CHECK-NEXT:    movdqa {{.*#+}} xmm1 = [41,41,41,41,41,41,41,41,41,41,41,41,41,41,41,41]
+; CHECK-NEXT:    pminub %xmm0, %xmm1
 ; CHECK-NEXT:    pcmpeqb %xmm1, %xmm0
-; CHECK-NEXT:    pcmpeqd %xmm1, %xmm1
-; CHECK-NEXT:    pxor %xmm1, %xmm0
 ; CHECK-NEXT:    retq
   %cmp = icmp ult <16 x i8> %x, <i8 42, i8 42, i8 42, i8 42, i8 42, i8 42, i8 42, i8 42, i8 42, i8 42, i8 42, i8 42, i8 42, i8 42, i8 42, i8 42>
   ret <16 x i1> %cmp
 }
 
 define <8 x i1> @ult_v8i16_splat(<8 x i16> %x) {
 ; SSE2-LABEL: ult_v8i16_splat:
 ; SSE2:       ## %bb.0:
 ; SSE2-NEXT:    psubusw {{.*}}(%rip), %xmm0
 ; SSE2-NEXT:    pxor %xmm1, %xmm1
 ; SSE2-NEXT:    pcmpeqw %xmm1, %xmm0
 ; SSE2-NEXT:    retq
 ;
 ; SSE41-LABEL: ult_v8i16_splat:
 ; SSE41:       ## %bb.0:
-; SSE41-NEXT:    movdqa {{.*#+}} xmm1 = [242,242,242,242,242,242,242,242]
-; SSE41-NEXT:    pmaxuw %xmm0, %xmm1
+; SSE41-NEXT:    movdqa {{.*#+}} xmm1 = [241,241,241,241,241,241,241,241]
+; SSE41-NEXT:    pminuw %xmm0, %xmm1
 ; SSE41-NEXT:    pcmpeqw %xmm1, %xmm0
-; SSE41-NEXT:    pcmpeqd %xmm1, %xmm1
-; SSE41-NEXT:    pxor %xmm1, %xmm0
 ; SSE41-NEXT:    retq
   %cmp = icmp ult <8 x i16> %x, <i16 242, i16 242, i16 242, i16 242, i16 242, i16 242, i16 242, i16 242>
   ret <8 x i1> %cmp
 }
 
 define <4 x i1> @ult_v4i32_splat(<4 x i32> %x) {
 ; SSE2-LABEL: ult_v4i32_splat:
 ; SSE2:       ## %bb.0:
 ; SSE2-NEXT:    pxor {{.*}}(%rip), %xmm0
 ; SSE2-NEXT:    movdqa {{.*#+}} xmm1 = [2147483606,2147483606,2147483606,2147483606]
 ; SSE2-NEXT:    pcmpgtd %xmm0, %xmm1
 ; SSE2-NEXT:    movdqa %xmm1, %xmm0
 ; SSE2-NEXT:    retq
 ;
 ; SSE41-LABEL: ult_v4i32_splat:
 ; SSE41:       ## %bb.0:
-; SSE41-NEXT:    movdqa {{.*#+}} xmm1 = [4294967254,4294967254,4294967254,4294967254]
-; SSE41-NEXT:    pmaxud %xmm0, %xmm1
+; SSE41-NEXT:    movdqa {{.*#+}} xmm1 = [4294967253,4294967253,4294967253,4294967253]
+; SSE41-NEXT:    pminud %xmm0, %xmm1
 ; SSE41-NEXT:    pcmpeqd %xmm1, %xmm0
-; SSE41-NEXT:    pcmpeqd %xmm1, %xmm1
-; SSE41-NEXT:    pxor %xmm1, %xmm0
 ; SSE41-NEXT:    retq
   %cmp = icmp ult <4 x i32> %x, <i32 -42, i32 -42, i32 -42, i32 -42>
   ret <4 x i1> %cmp
 }
 
 define <2 x i1> @ult_v2i64_splat(<2 x i64> %x) {
 ; SSE2-LABEL: ult_v2i64_splat:
 ; SSE2:       ## %bb.0:

 ; SSE2-NEXT:    pxor {{.*}}(%rip), %xmm0
 ; SSE2-NEXT:    movdqa {{.*#+}} xmm1 = [2147483652,2147483652,2147483652,2147483652]
 ; SSE2-NEXT:    pcmpgtd %xmm0, %xmm1
 ; SSE2-NEXT:    movdqa %xmm1, %xmm0
 ; SSE2-NEXT:    retq
 ;
 ; SSE41-LABEL: ugt_v4i32_splat_commute:
 ; SSE41:       ## %bb.0:
-; SSE41-NEXT:    movdqa {{.*#+}} xmm1 = [4,4,4,4]
-; SSE41-NEXT:    pmaxud %xmm0, %xmm1
+; SSE41-NEXT:    movdqa {{.*#+}} xmm1 = [3,3,3,3]
+; SSE41-NEXT:    pminud %xmm0, %xmm1
 ; SSE41-NEXT:    pcmpeqd %xmm1, %xmm0
-; SSE41-NEXT:    pcmpeqd %xmm1, %xmm1
-; SSE41-NEXT:    pxor %xmm1, %xmm0
 ; SSE41-NEXT:    retq
   %cmp = icmp ugt <4 x i32> <i32 4, i32 4, i32 4, i32 4>, %x
   ret <4 x i1> %cmp
 }
 
 define <8 x i16> @PR39859(<8 x i16> %x, <8 x i16> %y) {
 ; SSE2-LABEL: PR39859:
 ; SSE2:       ## %bb.0:
 ; SSE2-NEXT:    movdqa {{.*#+}} xmm2 = [32768,32768,32768,32768,32768,32768,32768,32768]
 ; SSE2-NEXT:    pxor %xmm0, %xmm2
 ; SSE2-NEXT:    pcmpgtw {{.*}}(%rip), %xmm2
 ; SSE2-NEXT:    pand %xmm2, %xmm1
 ; SSE2-NEXT:    pandn %xmm0, %xmm2
 ; SSE2-NEXT:    por %xmm1, %xmm2
 ; SSE2-NEXT:    movdqa %xmm2, %xmm0
 ; SSE2-NEXT:    retq
 ;
 ; SSE41-LABEL: PR39859:
 ; SSE41:       ## %bb.0:
 ; SSE41-NEXT:    movdqa %xmm0, %xmm2
-; SSE41-NEXT:    movdqa {{.*#+}} xmm3 = [42,42,42,42,42,42,42,42]
-; SSE41-NEXT:    pminuw %xmm0, %xmm3
-; SSE41-NEXT:    pcmpeqw %xmm0, %xmm3
-; SSE41-NEXT:    pcmpeqd %xmm0, %xmm0
-; SSE41-NEXT:    pxor %xmm3, %xmm0
+; SSE41-NEXT:    movdqa {{.*#+}} xmm0 = [43,43,43,43,43,43,43,43]
+; SSE41-NEXT:    pmaxuw %xmm2, %xmm0
+; SSE41-NEXT:    pcmpeqw %xmm2, %xmm0
 ; SSE41-NEXT:    pblendvb %xmm0, %xmm1, %xmm2
 ; SSE41-NEXT:    movdqa %xmm2, %xmm0
 ; SSE41-NEXT:    retq
   %cmp = icmp ugt <8 x i16> %x, <i16 42, i16 42, i16 42, i16 42, i16 42, i16 42, i16 42, i16 42>
   %sel = select <8 x i1> %cmp, <8 x i16> %y, <8 x i16> %x
   ret <8 x i16> %sel
 }