[PATCH v1 bpf-next 12/18] bpf: Follow integer casts in bpf_scan_ir

[Anton Protopopov <a.s.protopopov@gmail.com>]

Follow sign extensions and truncations between integers of at least 32
bits in the block of the return. They keep an error, for example an int
error which a function returns as long.

Signed-off-by: Anton Protopopov <a.s.protopopov@gmail.com>
---
 scripts/llvm-plugins/bpf_scan_ir.cpp | 28 +++++++++++++++++++++++++---
 1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/scripts/llvm-plugins/bpf_scan_ir.cpp b/scripts/llvm-plugins/bpf_scan_ir.cpp
index 81de8f941568..a3c6336662fc 100644
--- a/scripts/llvm-plugins/bpf_scan_ir.cpp
+++ b/scripts/llvm-plugins/bpf_scan_ir.cpp
@@ -82,17 +82,39 @@ static bool errnoConstant(const Value *V, int64_t &N)
 	return N >= -MaxErrno && N < 0;
 }
 
+/* A sign extension or a truncation between integers of at least 32 bits */
+static bool preservesErrnoCast(const CastInst *Cast)
+{
+	Type *Src = Cast->getSrcTy(), *Dst = Cast->getDestTy();
+
+	if (Src->isIntegerTy() && Dst->isIntegerTy())
+		return (Cast->getOpcode() == Instruction::SExt ||
+			Cast->getOpcode() == Instruction::Trunc) &&
+		       Src->getIntegerBitWidth() >= 32 && Dst->getIntegerBitWidth() >= 32;
+	return false;
+}
+
 /*
  * Add the errors which V, the value returned in RET, is known to be on the
- * edges to RET from CLEANBBS to VALUES. V may be a PHI in RET. A PHI in an
- * earlier block is not followed: a later branch may split its values between
- * clean and dirty paths.
+ * edges to RET from CLEANBBS to VALUES. Follow the casts in RET which keep the
+ * error to a PHI in RET. A PHI in an earlier block is not followed: a later
+ * branch may split its values between clean and dirty paths.
  */
 static void collectErrnos(Value *V, BasicBlock *Ret, LazyValueInfo &LVI,
 			  const SmallPtrSetImpl<BasicBlock *> &CleanBBs, ReturnValues &Values)
 {
 	int64_t N;
 
+	while (auto *Cast = dyn_cast<CastInst>(V)) {
+		if (Cast->getParent() != Ret || !preservesErrnoCast(Cast))
+			return;
+		if (singleErrnoAtUse(Cast->getOperandUse(0), LVI, N)) {
+			Values.push_back(N);
+			return;
+		}
+		V = Cast->getOperand(0);
+	}
+
 	auto *Phi = dyn_cast<PHINode>(V);
 
 	if (!Phi || Phi->getParent() != Ret)
-- 
2.43.0