[llvm] ec0f0ec - [RISCV] Add asserts that we don't increase codesize during pseudo expansion

[Philip Reames via llvm-commits]

Author: Philip Reames
Date: 2023-01-31T07:49:54-08:00
New Revision: ec0f0ecd48e99ebecd224585c04c67a177543fa1

URL: https://github.com/llvm/llvm-project/commit/ec0f0ecd48e99ebecd224585c04c67a177543fa1
DIFF: https://github.com/llvm/llvm-project/commit/ec0f0ecd48e99ebecd224585c04c67a177543fa1.diff

LOG: [RISCV] Add asserts that we don't increase codesize during pseudo expansion

We currently assume that pseudo expansion doesn't increase the distance between a branch and it's label. This patch adds some asserts to catch violations of this property in pseudo expansion.

I chose to only do the assertion at the function level as we have to scan the whole function for size changes (since expansion can create multiple blocks). We could cache individual block sizes, and thus make the check cheap enough to do after every expansion, but that requires more complex code.

Differential Revision: https://reviews.llvm.org/D142777

Added: 
    

Modified: 
    llvm/lib/Target/RISCV/RISCVExpandAtomicPseudoInsts.cpp
    llvm/lib/Target/RISCV/RISCVExpandPseudoInsts.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/RISCV/RISCVExpandAtomicPseudoInsts.cpp b/llvm/lib/Target/RISCV/RISCVExpandAtomicPseudoInsts.cpp
index 58ae28d57bd8..6a9b959fe4cd 100644
--- a/llvm/lib/Target/RISCV/RISCVExpandAtomicPseudoInsts.cpp
+++ b/llvm/lib/Target/RISCV/RISCVExpandAtomicPseudoInsts.cpp
@@ -58,15 +58,34 @@ class RISCVExpandAtomicPseudo : public MachineFunctionPass {
   bool expandAtomicCmpXchg(MachineBasicBlock &MBB,
                            MachineBasicBlock::iterator MBBI, bool IsMasked,
                            int Width, MachineBasicBlock::iterator &NextMBBI);
+#ifndef NDEBUG
+  unsigned getInstSizeInBytes(const MachineFunction &MF) const {
+    unsigned Size = 0;
+    for (auto &MBB : MF)
+      for (auto &MI : MBB)
+        Size += TII->getInstSizeInBytes(MI);
+    return Size;
+  }
+#endif
 };
 
 char RISCVExpandAtomicPseudo::ID = 0;
 
 bool RISCVExpandAtomicPseudo::runOnMachineFunction(MachineFunction &MF) {
   TII = static_cast<const RISCVInstrInfo *>(MF.getSubtarget().getInstrInfo());
+
+#ifndef NDEBUG
+  const unsigned OldSize = getInstSizeInBytes(MF);
+#endif
+
   bool Modified = false;
   for (auto &MBB : MF)
     Modified |= expandMBB(MBB);
+
+#ifndef NDEBUG
+  const unsigned NewSize = getInstSizeInBytes(MF);
+  assert(OldSize >= NewSize);
+#endif
   return Modified;
 }
 

diff  --git a/llvm/lib/Target/RISCV/RISCVExpandPseudoInsts.cpp b/llvm/lib/Target/RISCV/RISCVExpandPseudoInsts.cpp
index c4d85dc8ddc9..b8e4665bea91 100644
--- a/llvm/lib/Target/RISCV/RISCVExpandPseudoInsts.cpp
+++ b/llvm/lib/Target/RISCV/RISCVExpandPseudoInsts.cpp
@@ -50,15 +50,34 @@ class RISCVExpandPseudo : public MachineFunctionPass {
   bool expandVSetVL(MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI);
   bool expandVMSET_VMCLR(MachineBasicBlock &MBB,
                          MachineBasicBlock::iterator MBBI, unsigned Opcode);
+#ifndef NDEBUG
+  unsigned getInstSizeInBytes(const MachineFunction &MF) const {
+    unsigned Size = 0;
+    for (auto &MBB : MF)
+      for (auto &MI : MBB)
+        Size += TII->getInstSizeInBytes(MI);
+    return Size;
+  }
+#endif
 };
 
 char RISCVExpandPseudo::ID = 0;
 
 bool RISCVExpandPseudo::runOnMachineFunction(MachineFunction &MF) {
   TII = static_cast<const RISCVInstrInfo *>(MF.getSubtarget().getInstrInfo());
+
+#ifndef NDEBUG
+  const unsigned OldSize = getInstSizeInBytes(MF);
+#endif
+
   bool Modified = false;
   for (auto &MBB : MF)
     Modified |= expandMBB(MBB);
+
+#ifndef NDEBUG
+  const unsigned NewSize = getInstSizeInBytes(MF);
+  assert(OldSize >= NewSize);
+#endif
   return Modified;
 }
 
@@ -271,15 +290,34 @@ class RISCVPreRAExpandPseudo : public MachineFunctionPass {
   bool expandLoadTLSGDAddress(MachineBasicBlock &MBB,
                               MachineBasicBlock::iterator MBBI,
                               MachineBasicBlock::iterator &NextMBBI);
+#ifndef NDEBUG
+  unsigned getInstSizeInBytes(const MachineFunction &MF) const {
+    unsigned Size = 0;
+    for (auto &MBB : MF)
+      for (auto &MI : MBB)
+        Size += TII->getInstSizeInBytes(MI);
+    return Size;
+  }
+#endif
 };
 
 char RISCVPreRAExpandPseudo::ID = 0;
 
 bool RISCVPreRAExpandPseudo::runOnMachineFunction(MachineFunction &MF) {
   TII = static_cast<const RISCVInstrInfo *>(MF.getSubtarget().getInstrInfo());
+
+#ifndef NDEBUG
+  const unsigned OldSize = getInstSizeInBytes(MF);
+#endif
+
   bool Modified = false;
   for (auto &MBB : MF)
     Modified |= expandMBB(MBB);
+
+#ifndef NDEBUG
+  const unsigned NewSize = getInstSizeInBytes(MF);
+  assert(OldSize >= NewSize);
+#endif
   return Modified;
 }