[AMDGPU] Simplify setcc (sext from i1 b), -1|0, cc

[rampitec]

Summary

Depending on the compare code that can be either an argument of
sext or negate of it. This helps to avoid v_cndmask_b64 instruction
for sext. A reversed value can be further simplified and folded into
its parent comparison if possible.

[arsenm]

There are already an extensive number of combines that do this sort of thing in the generic DAGcombiner. Have you looked into why those aren't working? I know some are broken because they don't properly check the TargetBooalenContents

[rampitec]

In D34545#788670, @arsenm wrote:

There are already an extensive number of combines that do this sort of thing in the generic DAGcombiner. Have you looked into why those aren't working? I know some are broken because they don't properly check the TargetBooalenContents

These patterns are quite specific to our way of bool deserialization. Moreover, just like previous it is not always beneficial to do, it all depends where do we expect to have initial bool value.

[arsenm]

lib/Target/AMDGPU/SIISelLowering.cpp

4315 ↗

(On Diff #103672)

Deserialized isn't the right word. I think you mean an i1 which must be an in SGPR/condition register. Maybe isBoolSGPR or something?

5127–5135 ↗

(On Diff #103672)

Constants are canonicalized to the RHS as is, you shouldn't' need to handle this here

5137 ↗

(On Diff #103672)

CRHS condition first

[arsenm]

lib/Target/AMDGPU/SIISelLowering.cpp

5143 ↗

(On Diff #103672)

I don't think it is useful check the GT/LT cases. I would expect those to fold to eq/ne the bool value already

[rampitec]

lib/Target/AMDGPU/SIISelLowering.cpp

5127–5135 ↗

(On Diff #103672)

I agree, but I have seen a real case where it was swapped.

[rampitec]

lib/Target/AMDGPU/SIISelLowering.cpp

5143 ↗

(On Diff #103672)

It is not folded. At least not always.

[rampitec]

Renamed function and changed check order.

[vpykhtin]

LGTM.

llvm/trunk/lib/Target/AMDGPU/SIISelLowering.cpp

 SDValue SITargetLowering::performSetCCCombine(SDNode *N,
                                               DAGCombinerInfo &DCI) const {
   SelectionDAG &DAG = DCI.DAG;
   SDLoc SL(N);
 
   SDValue LHS = N->getOperand(0);
   SDValue RHS = N->getOperand(1);
   EVT VT = LHS.getValueType();
+  ISD::CondCode CC = cast<CondCodeSDNode>(N->getOperand(2))->get();
+
+  auto CRHS = dyn_cast<ConstantSDNode>(RHS);
+  if (!CRHS) {
+    CRHS = dyn_cast<ConstantSDNode>(LHS);
+    if (CRHS) {
+      std::swap(LHS, RHS);
+      CC = getSetCCSwappedOperands(CC);
+    }
+  }
+
+  if (CRHS && VT == MVT::i32 && LHS.getOpcode() == ISD::SIGN_EXTEND &&
+      isBoolSGPR(LHS.getOperand(0))) {
+    // setcc (sext from i1 cc), -1, ne|sgt|ult) => not cc => xor cc, -1
+    // setcc (sext from i1 cc), -1, eq|sle|uge) => cc
+    // setcc (sext from i1 cc),  0, eq|sge|ule) => not cc => xor cc, -1
+    // setcc (sext from i1 cc),  0, ne|ugt|slt) => cc
+    if ((CRHS->isAllOnesValue() &&
+         (CC == ISD::SETNE || CC == ISD::SETGT || CC == ISD::SETULT)) ||
+        (CRHS->isNullValue() &&
+         (CC == ISD::SETEQ || CC == ISD::SETGE || CC == ISD::SETULE)))
+      return DAG.getNode(ISD::XOR, SL, MVT::i1, LHS.getOperand(0),
+                         DAG.getConstant(-1, SL, MVT::i1));
+    if ((CRHS->isAllOnesValue() &&
+         (CC == ISD::SETEQ || CC == ISD::SETLE || CC == ISD::SETUGE)) ||
+        (CRHS->isNullValue() &&
+         (CC == ISD::SETNE || CC == ISD::SETUGT || CC == ISD::SETLT)))
+      return LHS.getOperand(0);
+  }
 
   if (VT != MVT::f32 && VT != MVT::f64 && (Subtarget->has16BitInsts() &&
                                            VT != MVT::f16))
     return SDValue();
 
   // Match isinf pattern
   // (fcmp oeq (fabs x), inf) -> (fp_class x, (p_infinity | n_infinity))
-  ISD::CondCode CC = cast<CondCodeSDNode>(N->getOperand(2))->get();
   if (CC == ISD::SETOEQ && LHS.getOpcode() == ISD::FABS) {
     const ConstantFPSDNode *CRHS = dyn_cast<ConstantFPSDNode>(RHS);
     if (!CRHS)
       return SDValue();
 
     const APFloat &APF = CRHS->getValueAPF();
     if (APF.isInfinity() && !APF.isNegative()) {
       unsigned Mask = SIInstrFlags::P_INFINITY | SIInstrFlags::N_INFINITY;

llvm/trunk/test/CodeGen/AMDGPU/setcc-sext.ll

+; RUN: llc -march=amdgcn -verify-machineinstrs < %s | FileCheck -check-prefix=GCN %s
+
+; GCN-LABEL: {{^}}setcc_sgt_true_sext:
+; GCN:      v_cmp_le_u32_e{{32|64}} [[CC:[^,]+]], v{{[0-9]+}}, v{{[0-9]+}}
+; GCN-NEXT: s_and_saveexec_b64 {{[^,]+}}, [[CC]]
+; GCN-NOT:  v_cndmask_
+
+define amdgpu_kernel void @setcc_sgt_true_sext(i32 addrspace(1)* nocapture %arg) {
+bb:
+  %x = tail call i32 @llvm.amdgcn.workitem.id.x()
+  %y = tail call i32 @llvm.amdgcn.workitem.id.y()
+  %cmp = icmp ugt i32 %x, %y
+  %ext = sext i1 %cmp to i32
+  %cond = icmp sgt i32 %ext, -1
+  br i1 %cond, label %then, label %endif
+
+then:
+  store i32 1, i32 addrspace(1)* %arg, align 4
+  br label %endif
+
+endif:
+  ret void
+}
+
+; GCN-LABEL: {{^}}setcc_sgt_true_sext_swap:
+; GCN:      v_cmp_le_u32_e{{32|64}} [[CC:[^,]+]], v{{[0-9]+}}, v{{[0-9]+}}
+; GCN-NEXT: s_and_saveexec_b64 {{[^,]+}}, [[CC]]
+; GCN-NOT:  v_cndmask_
+
+define amdgpu_kernel void @setcc_sgt_true_sext_swap(i32 addrspace(1)* nocapture %arg) {
+bb:
+  %x = tail call i32 @llvm.amdgcn.workitem.id.x()
+  %y = tail call i32 @llvm.amdgcn.workitem.id.y()
+  %cmp = icmp ugt i32 %x, %y
+  %ext = sext i1 %cmp to i32
+  %cond = icmp slt i32 -1, %ext
+  br i1 %cond, label %then, label %endif
+
+then:
+  store i32 1, i32 addrspace(1)* %arg, align 4
+  br label %endif
+
+endif:
+  ret void
+}
+
+; GCN-LABEL: {{^}}setcc_ne_true_sext:
+; GCN:      v_cmp_le_u32_e{{32|64}} [[CC:[^,]+]], v{{[0-9]+}}, v{{[0-9]+}}
+; GCN-NEXT: s_and_saveexec_b64 {{[^,]+}}, [[CC]]
+; GCN-NOT:  v_cndmask_
+
+define amdgpu_kernel void @setcc_ne_true_sext(i32 addrspace(1)* nocapture %arg) {
+bb:
+  %x = tail call i32 @llvm.amdgcn.workitem.id.x()
+  %y = tail call i32 @llvm.amdgcn.workitem.id.y()
+  %cmp = icmp ugt i32 %x, %y
+  %ext = sext i1 %cmp to i32
+  %cond = icmp ne i32 %ext, -1
+  br i1 %cond, label %then, label %endif
+
+then:
+  store i32 1, i32 addrspace(1)* %arg, align 4
+  br label %endif
+
+endif:
+  ret void
+}
+
+; GCN-LABEL: {{^}}setcc_ult_true_sext:
+; GCN:      v_cmp_le_u32_e{{32|64}} [[CC:[^,]+]], v{{[0-9]+}}, v{{[0-9]+}}
+; GCN-NEXT: s_and_saveexec_b64 {{[^,]+}}, [[CC]]
+; GCN-NOT:  v_cndmask_
+
+define amdgpu_kernel void @setcc_ult_true_sext(i32 addrspace(1)* nocapture %arg) {
+bb:
+  %x = tail call i32 @llvm.amdgcn.workitem.id.x()
+  %y = tail call i32 @llvm.amdgcn.workitem.id.y()
+  %cmp = icmp ugt i32 %x, %y
+  %ext = sext i1 %cmp to i32
+  %cond = icmp ult i32 %ext, -1
+  br i1 %cond, label %then, label %endif
+
+then:
+  store i32 1, i32 addrspace(1)* %arg, align 4
+  br label %endif
+
+endif:
+  ret void
+}
+
+; GCN-LABEL: {{^}}setcc_eq_true_sext:
+; GCN:      v_cmp_gt_u32_e{{32|64}} [[CC:[^,]+]], v{{[0-9]+}}, v{{[0-9]+}}
+; GCN-NEXT: s_and_saveexec_b64 {{[^,]+}}, [[CC]]
+; GCN-NOT:  v_cndmask_
+
+define amdgpu_kernel void @setcc_eq_true_sext(i32 addrspace(1)* nocapture %arg) {
+bb:
+  %x = tail call i32 @llvm.amdgcn.workitem.id.x()
+  %y = tail call i32 @llvm.amdgcn.workitem.id.y()
+  %cmp = icmp ugt i32 %x, %y
+  %ext = sext i1 %cmp to i32
+  %cond = icmp eq i32 %ext, -1
+  br i1 %cond, label %then, label %endif
+
+then:
+  store i32 1, i32 addrspace(1)* %arg, align 4
+  br label %endif
+
+endif:
+  ret void
+}
+
+; GCN-LABEL: {{^}}setcc_sle_true_sext:
+; GCN:      v_cmp_gt_u32_e{{32|64}} [[CC:[^,]+]], v{{[0-9]+}}, v{{[0-9]+}}
+; GCN-NEXT: s_and_saveexec_b64 {{[^,]+}}, [[CC]]
+; GCN-NOT:  v_cndmask_
+
+define amdgpu_kernel void @setcc_sle_true_sext(i32 addrspace(1)* nocapture %arg) {
+bb:
+  %x = tail call i32 @llvm.amdgcn.workitem.id.x()
+  %y = tail call i32 @llvm.amdgcn.workitem.id.y()
+  %cmp = icmp ugt i32 %x, %y
+  %ext = sext i1 %cmp to i32
+  %cond = icmp sle i32 %ext, -1
+  br i1 %cond, label %then, label %endif
+
+then:
+  store i32 1, i32 addrspace(1)* %arg, align 4
+  br label %endif
+
+endif:
+  ret void
+}
+
+; GCN-LABEL: {{^}}setcc_uge_true_sext:
+; GCN:      v_cmp_gt_u32_e{{32|64}} [[CC:[^,]+]], v{{[0-9]+}}, v{{[0-9]+}}
+; GCN-NEXT: s_and_saveexec_b64 {{[^,]+}}, [[CC]]
+; GCN-NOT:  v_cndmask_
+
+define amdgpu_kernel void @setcc_uge_true_sext(i32 addrspace(1)* nocapture %arg) {
+bb:
+  %x = tail call i32 @llvm.amdgcn.workitem.id.x()
+  %y = tail call i32 @llvm.amdgcn.workitem.id.y()
+  %cmp = icmp ugt i32 %x, %y
+  %ext = sext i1 %cmp to i32
+  %cond = icmp uge i32 %ext, -1
+  br i1 %cond, label %then, label %endif
+
+then:
+  store i32 1, i32 addrspace(1)* %arg, align 4
+  br label %endif
+
+endif:
+  ret void
+}
+
+; GCN-LABEL: {{^}}setcc_eq_false_sext:
+; GCN:      v_cmp_le_u32_e{{32|64}} [[CC:[^,]+]], v{{[0-9]+}}, v{{[0-9]+}}
+; GCN-NEXT: s_and_saveexec_b64 {{[^,]+}}, [[CC]]
+; GCN-NOT:  v_cndmask_
+
+define amdgpu_kernel void @setcc_eq_false_sext(i32 addrspace(1)* nocapture %arg) {
+bb:
+  %x = tail call i32 @llvm.amdgcn.workitem.id.x()
+  %y = tail call i32 @llvm.amdgcn.workitem.id.y()
+  %cmp = icmp ugt i32 %x, %y
+  %ext = sext i1 %cmp to i32
+  %cond = icmp eq i32 %ext, 0
+  br i1 %cond, label %then, label %endif
+
+then:
+  store i32 1, i32 addrspace(1)* %arg, align 4
+  br label %endif
+
+endif:
+  ret void
+}
+
+; GCN-LABEL: {{^}}setcc_sge_false_sext:
+; GCN:      v_cmp_le_u32_e{{32|64}} [[CC:[^,]+]], v{{[0-9]+}}, v{{[0-9]+}}
+; GCN-NEXT: s_and_saveexec_b64 {{[^,]+}}, [[CC]]
+; GCN-NOT:  v_cndmask_
+
+define amdgpu_kernel void @setcc_sge_false_sext(i32 addrspace(1)* nocapture %arg) {
+bb:
+  %x = tail call i32 @llvm.amdgcn.workitem.id.x()
+  %y = tail call i32 @llvm.amdgcn.workitem.id.y()
+  %cmp = icmp ugt i32 %x, %y
+  %ext = sext i1 %cmp to i32
+  %cond = icmp sge i32 %ext, 0
+  br i1 %cond, label %then, label %endif
+
+then:
+  store i32 1, i32 addrspace(1)* %arg, align 4
+  br label %endif
+
+endif:
+  ret void
+}
+
+; GCN-LABEL: {{^}}setcc_ule_false_sext:
+; GCN:      v_cmp_le_u32_e{{32|64}} [[CC:[^,]+]], v{{[0-9]+}}, v{{[0-9]+}}
+; GCN-NEXT: s_and_saveexec_b64 {{[^,]+}}, [[CC]]
+; GCN-NOT:  v_cndmask_
+
+define amdgpu_kernel void @setcc_ule_false_sext(i32 addrspace(1)* nocapture %arg) {
+bb:
+  %x = tail call i32 @llvm.amdgcn.workitem.id.x()
+  %y = tail call i32 @llvm.amdgcn.workitem.id.y()
+  %cmp = icmp ugt i32 %x, %y
+  %ext = sext i1 %cmp to i32
+  %cond = icmp ule i32 %ext, 0
+  br i1 %cond, label %then, label %endif
+
+then:
+  store i32 1, i32 addrspace(1)* %arg, align 4
+  br label %endif
+
+endif:
+  ret void
+}
+
+; GCN-LABEL: {{^}}setcc_ne_false_sext:
+; GCN:      v_cmp_gt_u32_e{{32|64}} [[CC:[^,]+]], v{{[0-9]+}}, v{{[0-9]+}}
+; GCN-NEXT: s_and_saveexec_b64 {{[^,]+}}, [[CC]]
+; GCN-NOT:  v_cndmask_
+
+define amdgpu_kernel void @setcc_ne_false_sext(i32 addrspace(1)* nocapture %arg) {
+bb:
+  %x = tail call i32 @llvm.amdgcn.workitem.id.x()
+  %y = tail call i32 @llvm.amdgcn.workitem.id.y()
+  %cmp = icmp ugt i32 %x, %y
+  %ext = sext i1 %cmp to i32
+  %cond = icmp ne i32 %ext, 0
+  br i1 %cond, label %then, label %endif
+
+then:
+  store i32 1, i32 addrspace(1)* %arg, align 4
+  br label %endif
+
+endif:
+  ret void
+}
+; GCN-LABEL: {{^}}setcc_ugt_false_sext:
+; GCN:      v_cmp_gt_u32_e{{32|64}} [[CC:[^,]+]], v{{[0-9]+}}, v{{[0-9]+}}
+; GCN-NEXT: s_and_saveexec_b64 {{[^,]+}}, [[CC]]
+; GCN-NOT:  v_cndmask_
+
+define amdgpu_kernel void @setcc_ugt_false_sext(i32 addrspace(1)* nocapture %arg) {
+bb:
+  %x = tail call i32 @llvm.amdgcn.workitem.id.x()
+  %y = tail call i32 @llvm.amdgcn.workitem.id.y()
+  %cmp = icmp ugt i32 %x, %y
+  %ext = sext i1 %cmp to i32
+  %cond = icmp ugt i32 %ext, 0
+  br i1 %cond, label %then, label %endif
+
+then:
+  store i32 1, i32 addrspace(1)* %arg, align 4
+  br label %endif
+
+endif:
+  ret void
+}
+; GCN-LABEL: {{^}}setcc_slt_false_sext:
+; GCN:      v_cmp_gt_u32_e{{32|64}} [[CC:[^,]+]], v{{[0-9]+}}, v{{[0-9]+}}
+; GCN-NEXT: s_and_saveexec_b64 {{[^,]+}}, [[CC]]
+; GCN-NOT:  v_cndmask_
+
+define amdgpu_kernel void @setcc_slt_false_sext(i32 addrspace(1)* nocapture %arg) {
+bb:
+  %x = tail call i32 @llvm.amdgcn.workitem.id.x()
+  %y = tail call i32 @llvm.amdgcn.workitem.id.y()
+  %cmp = icmp ugt i32 %x, %y
+  %ext = sext i1 %cmp to i32
+  %cond = icmp slt i32 %ext, 0
+  br i1 %cond, label %then, label %endif
+
+then:
+  store i32 1, i32 addrspace(1)* %arg, align 4
+  br label %endif
+
+endif:
+  ret void
+}
+
+
+declare i32 @llvm.amdgcn.workitem.id.x() #0
+
+declare i32 @llvm.amdgcn.workitem.id.y() #0
+
+attributes #0 = { nounwind readnone speculatable }