[mips][FastISel] Apply only zero-extension to constants prior to their materialization.

Summary:
Previously, we would sign-extend non-boolean negative constants and
zero-extend otherwise. This was problematic for PHI instructions with
negative values that had a type with bitwidth less than that of the
register used for materialization.

More specifically, ComputePHILiveOutRegInfo() assumes the constants
present in a PHI node are zero extended in their container and
afterwards deduces the known bits.

For example, previously we would materialize an i16 -4 with the
following instruction:

  addiu $r, $zero, -4

The register would end-up with the 32-bit 2's complement representation
of -4. However, ComputePHILiveOutRegInfo() would generate a constant
with the upper 16-bits set to zero. The SelectionDAG builder would use
that information to generate an AssertZero node that would remove any
subsequent trunc & zero_extend nodes.

In theory, we should modify ComputePHILiveOutRegInfo() to consult
target-specific hooks about the way they prefer to materialize the
given constants. However, git-blame reports that this specific code
has not been touched since 2011 and it seems to be working well for every
target so far.

Reviewers: dsanders

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D11592

llvm-svn: 243636

2 files changed, 14 insertions, 13 deletions

diff --git a/llvm/test/CodeGen/Mips/Fast-ISel/logopm.ll b/llvm/test/CodeGen/Mips/Fast-ISel/logopm.ll
index 0f0c3bf9e1d..42a1c43d893 100644
--- a/llvm/test/CodeGen/Mips/Fast-ISel/logopm.ll
+++ b/llvm/test/CodeGen/Mips/Fast-ISel/logopm.ll
@@ -283,8 +283,8 @@ entry:
 ; CHECK-DAG:    lw      $[[UC_ADDR:[0-9]+]], %got(uc)($[[REG_GP]])
 ; CHECK-DAG:    lw      $[[UC1_ADDR:[0-9]+]], %got(uc1)($[[REG_GP]])
 ; CHECK-DAG:    lbu     $[[UC1:[0-9]+]], 0($[[UC1_ADDR]])
-; CHECK-DAG:    addiu   $[[CONST_Neg89:[0-9]+]], $zero, -89
-; CHECK-DAG:    and     $[[RES:[0-9]+]], $[[UC1]], $[[CONST_Neg89]]
+; CHECK-DAG:    addiu   $[[CONST_167:[0-9]+]], $zero, 167
+; CHECK-DAG:    and     $[[RES:[0-9]+]], $[[UC1]], $[[CONST_167]]
 ; CHECK:        sb      $[[RES]], 0($[[UC_ADDR]])
 ; CHECK:        .end    andUc1
   ret void
@@ -345,8 +345,8 @@ entry:
 ; CHECK-DAG:    lw      $[[UC_ADDR:[0-9]+]], %got(uc)($[[REG_GP]])
 ; CHECK-DAG:    lw      $[[UC1_ADDR:[0-9]+]], %got(uc1)($[[REG_GP]])
 ; CHECK-DAG:    lbu     $[[UC1:[0-9]+]], 0($[[UC1_ADDR]])
-; CHECK-DAG:    addiu   $[[CONST_neg18:[0-9]+]], $zero, -18
-; CHECK-DAG:    or      $[[RES:[0-9]+]], $[[UC1]], $[[CONST_neg18]]
+; CHECK-DAG:    addiu   $[[CONST_238:[0-9]+]], $zero, 238
+; CHECK-DAG:    or      $[[RES:[0-9]+]], $[[UC1]], $[[CONST_238]]
 ; CHECK:        sb      $[[RES]], 0($[[UC_ADDR]])
 ; CHECK:        .end    orUc1
   ret void
@@ -469,8 +469,8 @@ entry:
 ; CHECK-DAG:    lw      $[[US_ADDR:[0-9]+]], %got(us)($[[REG_GP]])
 ; CHECK-DAG:    lw      $[[US1_ADDR:[0-9]+]], %got(us1)($[[REG_GP]])
 ; CHECK-DAG:    lhu     $[[US1:[0-9]+]], 0($[[US1_ADDR]])
-; CHECK-DAG:    addiu   $[[CONST_Neg4185:[0-9]+]], $zero, -4185
-; CHECK-DAG:    and     $[[RES:[0-9]+]], $[[US1]], $[[CONST_Neg4185]]
+; CHECK-DAG:    ori     $[[CONST_61351:[0-9]+]], $zero, 61351
+; CHECK-DAG:    and     $[[RES:[0-9]+]], $[[US1]], $[[CONST_61351]]
 ; CHECK:        sh      $[[RES]], 0($[[US_ADDR]])
 ; CHECK:        .end    andUs1
   ret void
@@ -520,8 +520,8 @@ entry:
 ; CHECK-DAG:    lw      $[[US_ADDR:[0-9]+]], %got(us)($[[REG_GP]])
 ; CHECK-DAG:    lw      $[[US1_ADDR:[0-9]+]], %got(us1)($[[REG_GP]])
 ; CHECK-DAG:    lhu     $[[US1:[0-9]+]], 0($[[US1_ADDR]])
-; CHECK-DAG:    addiu   $[[CONST_neg4591:[0-9]+]], $zero, -4591
-; CHECK-DAG:    or      $[[RES:[0-9]+]], $[[US1]], $[[CONST_neg4591]]
+; CHECK-DAG:    ori     $[[CONST_60945:[0-9]+]], $zero, 60945
+; CHECK-DAG:    or      $[[RES:[0-9]+]], $[[US1]], $[[CONST_60945]]
 ; CHECK:        sh      $[[RES]], 0($[[US_ADDR]])
 ; CHECK:        .end    orUs1
   ret void
@@ -583,8 +583,8 @@ entry:
 ; CHECK-DAG:    lw      $[[US_ADDR:[0-9]+]], %got(us)($[[REG_GP]])
 ; CHECK-DAG:    lw      $[[US1_ADDR:[0-9]+]], %got(us1)($[[REG_GP]])
 ; CHECK-DAG:    lhu     $[[US1:[0-9]+]], 0($[[US1_ADDR]])
-; CHECK-DAG:    addiu   $[[CONST_Neg5512:[0-9]+]], $zero, -5512
-; CHECK-DAG:    xor     $[[RES:[0-9]+]], $[[US1]], $[[CONST_Neg5512]]
+; CHECK-DAG:    ori     $[[CONST_60024:[0-9]+]], $zero, 60024
+; CHECK-DAG:    xor     $[[RES:[0-9]+]], $[[US1]], $[[CONST_60024]]
 ; CHECK:        sh      $[[RES]], 0($[[US_ADDR]])
 ; CHECK:        .end    xorUs1
   ret void
diff --git a/llvm/test/CodeGen/Mips/Fast-ISel/simplestorei.ll b/llvm/test/CodeGen/Mips/Fast-ISel/simplestorei.ll
index 83ccae0b1de..d8c03f22f9b 100644
--- a/llvm/test/CodeGen/Mips/Fast-ISel/simplestorei.ll
+++ b/llvm/test/CodeGen/Mips/Fast-ISel/simplestorei.ll
@@ -22,9 +22,10 @@ define void @si2_2() #0 {
 entry:
   store i32 -32768, i32* @ijk, align 4
 ; CHECK:        .ent    si2_2
-; CHECK:        addiu   $[[REG1:[0-9]+]], $zero, -32768
-; CHECK:        lw      $[[REG2:[0-9]+]], %got(ijk)(${{[0-9]+}})
-; CHECK:        sw      $[[REG1]], 0($[[REG2]])
+; CHECK:        lui     $[[REG1:[0-9]+]], 65535
+; CHECK:        ori     $[[REG2:[0-9]+]], $[[REG1]], 32768
+; CHECK:        lw      $[[REG3:[0-9]+]], %got(ijk)(${{[0-9]+}})
+; CHECK:        sw      $[[REG2]], 0($[[REG3]])
   ret void
 }