Revert "[DAG] SimplifyDemandedBits - if we're only demanding the signbit, a SMIN/SMAX node can be simplified to a OR/AND node respectively."

This reverts commit 54d663d, which breaks the test CodeGen/SystemZ/ctpop-01.ll for stage2-ubsan check (see https://lab.llvm.org/buildbot/#/builders/85/builds/18410)

I manually confirmed that the test had been passing immediately prior to that commit
(BUILDBOT_REVISION=4772c66cfb00d60f8f687930e9dd3aa1b6872228 llvm-zorg/zorg/buildbot/builders/sanitizers/buildbot_bootstrap_ubsan.sh)

Author: thurstond

llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

@@ -1688,22 +1688,6 @@ bool TargetLowering::SimplifyDemandedBits(
       Known.Zero.setBitsFrom(1);
     break;
   }
-  case ISD::SMIN: {
-    SDValue Op0 = Op.getOperand(0);
-    SDValue Op1 = Op.getOperand(1);
-    // If we're only wanting the signbit, then we can simplify to OR node.
-    if (OriginalDemandedBits.isSignMask())
-      return TLO.CombineTo(Op, TLO.DAG.getNode(ISD::OR, dl, VT, Op0, Op1));
-    break;
-  }
-  case ISD::SMAX: {
-    SDValue Op0 = Op.getOperand(0);
-    SDValue Op1 = Op.getOperand(1);
-    // If we're only wanting the signbit, then we can simplify to AND node.
-    if (OriginalDemandedBits.isSignMask())
-      return TLO.CombineTo(Op, TLO.DAG.getNode(ISD::AND, dl, VT, Op0, Op1));
-    break;
-  }
   case ISD::SHL: {
     SDValue Op0 = Op.getOperand(0);
     SDValue Op1 = Op.getOperand(1);

llvm/test/CodeGen/X86/smax.ll

@@ -692,7 +692,9 @@ define i64 @test_signbits_i64(i64 %a, i64 %b) nounwind {
 ; X86-LABEL: test_signbits_i64:
 ; X86:       # %bb.0:
 ; X86-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; X86-NEXT:    andl {{[0-9]+}}(%esp), %eax
+; X86-NEXT:    movl {{[0-9]+}}(%esp), %ecx
+; X86-NEXT:    cmpl %eax, %ecx
+; X86-NEXT:    cmovgl %ecx, %eax
 ; X86-NEXT:    movl %eax, %edx
 ; X86-NEXT:    sarl $31, %edx
 ; X86-NEXT:    retl
@@ -707,7 +709,8 @@ define i128 @test_signbits_i128(i128 %a, i128 %b) nounwind {
 ; X64:       # %bb.0:
 ; X64-NEXT:    movq %rcx, %rax
 ; X64-NEXT:    sarq $28, %rax
-; X64-NEXT:    andq %rsi, %rax
+; X64-NEXT:    cmpq %rax, %rsi
+; X64-NEXT:    cmovgq %rsi, %rax
 ; X64-NEXT:    movq %rax, %rdx
 ; X64-NEXT:    sarq $63, %rdx
 ; X64-NEXT:    retq

llvm/test/CodeGen/X86/smin.ll

@@ -693,7 +693,9 @@ define i64 @test_signbits_i64(i64 %a, i64 %b) nounwind {
 ; X86-LABEL: test_signbits_i64:
 ; X86:       # %bb.0:
 ; X86-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; X86-NEXT:    orl {{[0-9]+}}(%esp), %eax
+; X86-NEXT:    movl {{[0-9]+}}(%esp), %ecx
+; X86-NEXT:    cmpl %eax, %ecx
+; X86-NEXT:    cmovll %ecx, %eax
 ; X86-NEXT:    movl %eax, %edx
 ; X86-NEXT:    sarl $31, %edx
 ; X86-NEXT:    retl
@@ -708,7 +710,8 @@ define i128 @test_signbits_i128(i128 %a, i128 %b) nounwind {
 ; X64:       # %bb.0:
 ; X64-NEXT:    movq %rcx, %rax
 ; X64-NEXT:    sarq $28, %rax
-; X64-NEXT:    orq %rsi, %rax
+; X64-NEXT:    cmpq %rax, %rsi
+; X64-NEXT:    cmovlq %rsi, %rax
 ; X64-NEXT:    movq %rax, %rdx
 ; X64-NEXT:    sarq $63, %rdx
 ; X64-NEXT:    retq