[llvm] r371434 - [IfConversion] Correctly handle cases where analyzeBranch fails.

[Eli Friedman via llvm-commits]

Author: efriedma
Date: Mon Sep  9 11:29:27 2019
New Revision: 371434

URL: http://llvm.org/viewvc/llvm-project?rev=371434&view=rev
Log:
[IfConversion] Correctly handle cases where analyzeBranch fails.

If analyzeBranch fails, on some targets, the out parameters point to
some blocks in the function. But we can't use that information, so make
sure to clear it out.  (In some places in IfConversion, we assume that
any block with a TrueBB is analyzable.)

The change to the testcase makes it trigger a bug on builds without this
fix: IfConvertDiamond tries to perform a followup "merge" operation,
which isn't legal, and we somehow end up with a branch to a deleted MBB.
I'm not sure how this doesn't crash the compiler.

Differential Revision: https://reviews.llvm.org/D67306


Modified:
    llvm/trunk/lib/CodeGen/IfConversion.cpp
    llvm/trunk/test/CodeGen/ARM/ifcvt-diamond-unanalyzable-common.mir

Modified: llvm/trunk/lib/CodeGen/IfConversion.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/IfConversion.cpp?rev=371434&r1=371433&r2=371434&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/IfConversion.cpp (original)
+++ llvm/trunk/lib/CodeGen/IfConversion.cpp Mon Sep  9 11:29:27 2019
@@ -912,6 +912,12 @@ void IfConverter::AnalyzeBranches(BBInfo
   BBI.BrCond.clear();
   BBI.IsBrAnalyzable =
       !TII->analyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
+  if (!BBI.IsBrAnalyzable) {
+    BBI.TrueBB = nullptr;
+    BBI.FalseBB = nullptr;
+    BBI.BrCond.clear();
+  }
+
   SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
   BBI.IsBrReversible = (RevCond.size() == 0) ||
       !TII->reverseBranchCondition(RevCond);

Modified: llvm/trunk/test/CodeGen/ARM/ifcvt-diamond-unanalyzable-common.mir
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/ifcvt-diamond-unanalyzable-common.mir?rev=371434&r1=371433&r2=371434&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/ARM/ifcvt-diamond-unanalyzable-common.mir (original)
+++ llvm/trunk/test/CodeGen/ARM/ifcvt-diamond-unanalyzable-common.mir Mon Sep  9 11:29:27 2019
@@ -1,4 +1,4 @@
-# RUN: llc %s -o - -run-pass=if-converter | FileCheck %s
+# RUN: llc %s -o - -run-pass=if-converter -verify-machineinstrs | FileCheck %s
 # Make sure we correctly if-convert blocks containing an INLINEASM_BR.
 # CHECK: t2CMPri killed renamable $r2, 34
 # CHECK-NEXT: $r0 = t2MOVi 2, 1, $cpsr, $noreg
@@ -48,9 +48,8 @@ body:             |
     t2B %bb.3, 14, $noreg
   
   bb.3:
-    successors: %bb.4(0x80000000)
-  
     INLINEASM &"", 1
+    $sp = t2LDMIA_RET $sp, 14, $noreg, def $r4, def $pc
   
   bb.4.l_yes (address-taken):
     $sp = t2LDMIA_RET $sp, 14, $noreg, def $r4, def $pc