[BPI] Look through bitcasts in calcZeroHeuristic

[weiwang]

Summary

Constant hoisting may hide the constant value behind bitcast for And's
operand. Track down the constant to make the BFI result consistent
regardless of hoisting.

[samparker]

Thanks. It's okay to commit cleanup NFCs without review, so don't worry about these kind of patches up for review in the future.

[samparker]

But now I understand that this isn't an NFC! So can you add a test please?

[weiwang]

add test case

llvm/lib/Analysis/BranchProbabilityInfo.cpp

bool BranchProbabilityInfo::calcZeroHeuristics(const BasicBlock *BB,
   ConstantInt *CV = GetConstantInt(RHS);
   if (!CV)
     return false;
 
   // If the LHS is the result of AND'ing a value with a single bit bitmask,
   // we don't have information about probabilities.
   if (Instruction *LHS = dyn_cast<Instruction>(CI->getOperand(0)))
     if (LHS->getOpcode() == Instruction::And)
-      if (ConstantInt *AndRHS = dyn_cast<ConstantInt>(LHS->getOperand(1)))
+      if (ConstantInt *AndRHS = GetConstantInt(LHS->getOperand(1)))
         if (AndRHS->getValue().isPowerOf2())
           return false;
 
   // Check if the LHS is the return value of a library function
   LibFunc Func = NumLibFuncs;
   if (TLI)
     if (CallInst *Call = dyn_cast<CallInst>(CI->getOperand(0)))
       if (Function *CalledFn = Call->getCalledFunction())

llvm/test/Analysis/BranchProbabilityInfo/hoist.ll

+; RUN: opt < %s -analyze -branch-prob -enable-new-pm=0 | FileCheck %s
+; RUN: opt < %s -passes='print<branch-prob>' -disable-output 2>&1 | FileCheck %s
+
+; CHECK-LABEL: no_hoist
+; CHECK: edge entry -> if.end probability is 0x40000000 / 0x80000000 = 50.00%
+; CHECK: edge entry -> if.then probability is 0x40000000 / 0x80000000 = 50.00%
+; CHECK: edge if.end -> if.end4 probability is 0x40000000 / 0x80000000 = 50.00%
+; CHECK: edge if.end -> if.then3 probability is 0x40000000 / 0x80000000 = 50.00%
+define dso_local void @no_hoist(i64 %arg1, i64 %arg2) local_unnamed_addr #0 {
+entry:
+  %and = and i64 %arg1, 1152921504606846976
+  %tobool.not = icmp eq i64 %and, 0
+  br i1 %tobool.not, label %if.end, label %if.then
+
+if.then:                                          ; preds = %entry
+  tail call void @bar()
+  br label %if.end
+
+if.end:                                           ; preds = %if.then, %entry
+  %and1 = and i64 %arg2, 1152921504606846976
+  %tobool2.not = icmp eq i64 %and1, 0
+  br i1 %tobool2.not, label %if.end4, label %if.then3
+
+if.then3:                                         ; preds = %if.end
+  tail call void @baz()
+  br label %if.end4
+
+if.end4:                                          ; preds = %if.then3, %if.end
+  ret void
+}
+
+; CHECK-LABEL: hoist
+; CHECK: edge entry -> if.end probability is 0x40000000 / 0x80000000 = 50.00%
+; CHECK: edge entry -> if.then probability is 0x40000000 / 0x80000000 = 50.00%
+; CHECK: edge if.end -> if.end4 probability is 0x40000000 / 0x80000000 = 50.00%
+; CHECK: edge if.end -> if.then3 probability is 0x40000000 / 0x80000000 = 50.00%
+define dso_local void @hoist(i64 %arg1, i64 %arg2) local_unnamed_addr #0 {
+entry:
+  %const = bitcast i64 1152921504606846976 to i64
+  %and = and i64 %arg1, %const
+  %tobool.not = icmp eq i64 %and, 0
+  br i1 %tobool.not, label %if.end, label %if.then
+
+if.then:                                          ; preds = %entry
+  tail call void @bar()
+  br label %if.end
+
+if.end:                                           ; preds = %if.then, %entry
+  %and1 = and i64 %arg2, %const
+  %tobool2.not = icmp eq i64 %and1, 0
+  br i1 %tobool2.not, label %if.end4, label %if.then3
+
+if.then3:                                         ; preds = %if.end
+  tail call void @baz()
+  br label %if.end4
+
+if.end4:                                          ; preds = %if.then3, %if.end
+  ret void
+}
+
+declare dso_local void @bar() local_unnamed_addr #1
+
+declare dso_local void @baz() local_unnamed_addr #1