[SystemZ] Fix linux s390x main can't bootstrap itself on SanitizerSpecialCaseList.cpp #168088 (#168779)

This test has long call chain in recursion. Search tree can be pruned
early by swapping CC test and recursive simplifyAssumingCCVal.

Fixes: llvm/llvm-project#168088
Co-authored-by: anoopkg6 <[email protected]>
Signed-off-by: Hafidz Muzakky <[email protected]>

Author: 2 people

llvm/lib/Target/SystemZ/SystemZISelLowering.cpp

@@ -8673,15 +8673,17 @@ SmallVector<SDValue, 4> static simplifyAssumingCCVal(SDValue &Val, SDValue &CC,
 
     int CCValidVal = CCValid->getZExtValue();
     int CCMaskVal = CCMask->getZExtValue();
-    const auto &&TrueSDVals = simplifyAssumingCCVal(TrueVal, CC, DAG);
-    const auto &&FalseSDVals = simplifyAssumingCCVal(FalseVal, CC, DAG);
-    if (TrueSDVals.empty() || FalseSDVals.empty())
-      return {};
+    // Pruning search tree early - Moving CC test and combineCCMask ahead of
+    // recursive call to simplifyAssumingCCVal.
     SDValue Op4CCReg = Val.getOperand(4);
     if (Op4CCReg != CC)
       combineCCMask(Op4CCReg, CCValidVal, CCMaskVal, DAG);
     if (Op4CCReg != CC)
       return {};
+    const auto &&TrueSDVals = simplifyAssumingCCVal(TrueVal, CC, DAG);
+    const auto &&FalseSDVals = simplifyAssumingCCVal(FalseVal, CC, DAG);
+    if (TrueSDVals.empty() || FalseSDVals.empty())
+      return {};
     SmallVector<SDValue, 4> MergedSDVals;
     for (auto &CCVal : {0, 1, 2, 3})
       MergedSDVals.emplace_back(((CCMaskVal & (1 << (3 - CCVal))) != 0)