[ARM] Account for implicit IT when calculating inline asm size

When deciding if it is safe to optimize a conditional branch to a CBZ or
CBNZ the offsets of the BasicBlocks from the start of the function are
estimated. For inline assembly the generic getInlineAsmLength() function is
used to get a worst case estimate of the inline assembly by multiplying the
number of instructions by the max instruction size of 4 bytes. This
unfortunately doesn't take into account the generation of Thumb implicit IT
instructions. In edge cases such as when all the instructions in the block
are 4-bytes in size and there is an implicit IT then the size is
underestimated. This can cause an out of range CBZ or CBNZ to be generated.

The patch takes a conservative approach and assumes that every instruction
in the inline assembly block may have an implicit IT.

Fixes pr31805

Differential Revision: https://reviews.llvm.org/D52834

llvm-svn: 343960

diff --git a/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp b/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
index ac7d656..0d1908a 100644 (file)
--- a/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
+++ b/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
@@ -708,8 +708,12 @@ unsigned ARMBaseInstrInfo::getInstSizeInBytes(const MachineInstr &MI) const {
     return MCID.getSize();
 
   // If this machine instr is an inline asm, measure it.
-  if (MI.getOpcode() == ARM::INLINEASM)
-    return getInlineAsmLength(MI.getOperand(0).getSymbolName(), *MAI);
+  if (MI.getOpcode() == ARM::INLINEASM) {
+    unsigned Size = getInlineAsmLength(MI.getOperand(0).getSymbolName(), *MAI);
+    if (!MF->getInfo<ARMFunctionInfo>()->isThumbFunction())
+      Size = alignTo(Size, 4);
+    return Size;
+  }
   unsigned Opc = MI.getOpcode();
   switch (Opc) {
   default:

diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMMCAsmInfo.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMMCAsmInfo.cpp
index 0cef683..3ee63ac 100644 (file)
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMMCAsmInfo.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMMCAsmInfo.cpp
@@ -31,6 +31,9 @@ ARMMCAsmInfoDarwin::ARMMCAsmInfoDarwin(const Triple &TheTriple) {
 
   SupportsDebugInformation = true;
 
+  // Conditional Thumb 4-byte instructions can have an implicit IT.
+  MaxInstLength = 6;
+
   // Exceptions handling
   ExceptionsType = (TheTriple.isOSDarwin() && !TheTriple.isWatchABI())
                        ? ExceptionHandling::SjLj
@@ -56,6 +59,9 @@ ARMELFMCAsmInfo::ARMELFMCAsmInfo(const Triple &TheTriple) {
 
   SupportsDebugInformation = true;
 
+  // Conditional Thumb 4-byte instructions can have an implicit IT.
+  MaxInstLength = 6;
+
   // Exceptions handling
   switch (TheTriple.getOS()) {
   case Triple::NetBSD:
@@ -90,6 +96,9 @@ ARMCOFFMCAsmInfoMicrosoft::ARMCOFFMCAsmInfoMicrosoft() {
   PrivateGlobalPrefix = "$M";
   PrivateLabelPrefix = "$M";
   CommentString = ";";
+
+  // Conditional Thumb 4-byte instructions can have an implicit IT.
+  MaxInstLength = 6;
 }
 
 void ARMCOFFMCAsmInfoGNU::anchor() { }
@@ -110,5 +119,7 @@ ARMCOFFMCAsmInfoGNU::ARMCOFFMCAsmInfoGNU() {
 
   UseIntegratedAssembler = true;
   DwarfRegNumForCFI = false;
-}
 
+  // Conditional Thumb 4-byte instructions can have an implicit IT.
+  MaxInstLength = 6;
+}

diff --git a/llvm/test/CodeGen/ARM/cbz-implicit-it-range.ll b/llvm/test/CodeGen/ARM/cbz-implicit-it-range.ll
new file mode 100644 (file)
index 0000000..b553a9a
--- /dev/null
+++ b/llvm/test/CodeGen/ARM/cbz-implicit-it-range.ll
@@ -0,0 +1,47 @@
+;RUN: llc -O2 -mtriple=thumbv7a-linux-gnueabihf -arm-implicit-it=always %s -o - | FileCheck %s
+;RUN: llc -O2 -mtriple=thumbv7a-linux-gnueabihf -no-integrated-as %s -o - | FileCheck %s
+
+; Check that we do not produce a CBZ instruction to jump over the inline
+; assembly as the distance is too far if the implicit IT instructions are
+; added.
+
+define void @f0(i32 %p1, i32 %p2, i32 %p3) nounwind {
+entry:
+  %cmp = icmp eq i32 %p1, 0
+  br i1 %cmp, label %if.else, label %if.then
+
+if.then:
+  tail call void asm sideeffect "movseq r0, #0\0A", ""()
+  tail call void asm sideeffect "movseq r0, #0\0A", ""()
+  tail call void asm sideeffect "movseq r0, #0\0A", ""()
+  tail call void asm sideeffect "movseq r0, #0\0A", ""()
+  tail call void asm sideeffect "movseq r0, #0\0A", ""()
+  tail call void asm sideeffect "movseq r0, #0\0A", ""()
+  tail call void asm sideeffect "movseq r0, #0\0A", ""()
+  tail call void asm sideeffect "movseq r0, #0\0A", ""()
+  tail call void asm sideeffect "movseq r0, #0\0A", ""()
+  tail call void asm sideeffect "movseq r0, #0\0A", ""()
+  tail call void asm sideeffect "movseq r0, #0\0A", ""()
+  tail call void asm sideeffect "movseq r0, #0\0A", ""()
+  tail call void asm sideeffect "movseq r0, #0\0A", ""()
+  tail call void asm sideeffect "movseq r0, #0\0A", ""()
+  tail call void asm sideeffect "movseq r0, #0\0A", ""()
+  tail call void asm sideeffect "movseq r0, #0\0A", ""()
+  tail call void asm sideeffect "movseq r0, #0\0A", ""()
+  tail call void asm sideeffect "movseq r0, #0\0A", ""()
+  tail call void asm sideeffect "movseq r0, #0\0A", ""()
+  tail call void asm sideeffect "movseq r0, #0\0A", ""()
+  tail call void asm sideeffect "movseq r0, #0\0A", ""()
+  tail call void asm sideeffect "movseq r0, #0\0A", ""()
+  br label %if.end
+
+if.else:
+  tail call void asm sideeffect "nop\0A", ""()
+  br label %if.end
+
+if.end:
+  ret void
+}
+; CHECK-LABEL: f0:
+; CHECK: beq .LBB0_{{[0-9]+}}
+