[llvm] r285987 - Hoist check for TLI above all of the attempts to use it (including one

[Chandler Carruth via llvm-commits]

Author: chandlerc
Date: Fri Nov  4 01:54:00 2016
New Revision: 285987

URL: http://llvm.org/viewvc/llvm-project?rev=285987&view=rev
Log:
Hoist check for TLI above all of the attempts to use it (including one
of which that is hidden inside a separate function call) and helpfully
before building expensive transaction infrastructure. This will avoid
crashing when running CGP in a generic mode if we ever managed to hit
this case.

Note that I spent some time looking at alternatives. CGP is actually
used without a TM or TLI in order to do some target-independent testing.
Further, all of the neighboring optimization techniques actually have
some paths that are effective even in the absence of TLI so this seemed
the correct scope at which to check and bypass logic. It still isn't
clear that long-term support for missing TM/TLI is the right
cost/benefit tradeoff for CGP -- we seem to get relatively little for it
and the code is just littered with checks (and assumptions which
I suspect are still missing some checks).

This at least fixes the potential bug in this code spotted by
PVS-Studio, so we've got that going for us. ;]

Modified:
    llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp

Modified: llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp?rev=285987&r1=285986&r2=285987&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp (original)
+++ llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp Fri Nov  4 01:54:00 2016
@@ -4232,6 +4232,10 @@ bool CodeGenPrepare::extLdPromotion(Type
 /// promotions apply.
 ///
 bool CodeGenPrepare::moveExtToFormExtLoad(Instruction *&I) {
+  // ExtLoad formation infrastructure requires TLI to be effective.
+  if (!TLI)
+    return false;
+
   // Try to promote a chain of computation if it allows to form
   // an extended load.
   TypePromotionTransaction TPT;
@@ -4261,7 +4265,7 @@ bool CodeGenPrepare::moveExtToFormExtLoa
 
   // If the load has other users and the truncate is not free, this probably
   // isn't worthwhile.
-  if (!LI->hasOneUse() && TLI &&
+  if (!LI->hasOneUse() &&
       (TLI->isTypeLegal(LoadVT) || !TLI->isTypeLegal(VT)) &&
       !TLI->isTruncateFree(I->getType(), LI->getType())) {
     I = OldExt;
@@ -4277,7 +4281,7 @@ bool CodeGenPrepare::moveExtToFormExtLoa
     assert(isa<SExtInst>(I) && "Unexpected ext type!");
     LType = ISD::SEXTLOAD;
   }
-  if (TLI && !TLI->isLoadExtLegal(LType, VT, LoadVT)) {
+  if (!TLI->isLoadExtLegal(LType, VT, LoadVT)) {
     I = OldExt;
     TPT.rollback(LastKnownGood);
     return false;