[llvm] 116841c - RISCV: clean up target expression handling

[Saleem Abdulrasool via llvm-commits]

Author: Saleem Abdulrasool
Date: 2021-06-17T13:35:32-07:00
New Revision: 116841c623747972d0ae80239d3ea7b8409b868b

URL: https://github.com/llvm/llvm-project/commit/116841c623747972d0ae80239d3ea7b8409b868b
DIFF: https://github.com/llvm/llvm-project/commit/116841c623747972d0ae80239d3ea7b8409b868b.diff

LOG: RISCV: clean up target expression handling

The target specific expression handling was slightly regressed by
bbea64250f65480d787e1c5ff45c4de3ec2dcda8.  This restores the proper
sub-expression evaluation to allow for constant folding within the
expression.  We explicitly discard the layout and assembler when
evaluating the expression to avoid any symbolic computation and instead
using the `evaluateAsRelocatable` to canonicalise and constant fold
only.

We can also simplify the expression handling - none of the target
variants support symbolic difference.  This simplifies the logic for
that and adds additional tests to ensure that we do not accidentally
regress here in the future.

Reviewed By: maskray

Differential Revision: https://reviews.llvm.org/D104473

Added: 
    llvm/test/MC/RISCV/expressions.s

Modified: 
    llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCExpr.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCExpr.cpp b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCExpr.cpp
index 7bbf9be7fd9e6..65714b914c60a 100644
--- a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCExpr.cpp
+++ b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCExpr.cpp
@@ -92,33 +92,16 @@ const MCFixup *RISCVMCExpr::getPCRelHiFixup(const MCFragment **DFOut) const {
 bool RISCVMCExpr::evaluateAsRelocatableImpl(MCValue &Res,
                                             const MCAsmLayout *Layout,
                                             const MCFixup *Fixup) const {
-  bool IsSymbolicDifference = false;
-  if (const auto *MBE = dyn_cast<MCBinaryExpr>(getSubExpr())) {
-    if (isa<MCBinaryExpr>(MBE->getLHS()) && isa<MCConstantExpr>(MBE->getRHS()))
-      MBE = cast<MCBinaryExpr>(MBE->getLHS());
-    IsSymbolicDifference = isa<MCSymbolRefExpr>(MBE->getLHS()) &&
-                           isa<MCSymbolRefExpr>(MBE->getRHS());
-  }
+  // Explicitly drop the layout and assembler to prevent any symbolic folding in
+  // the expression handling.  This is required to preserve symbolic 
diff erence
+  // expressions to emit the paired relocations.
+  if (!getSubExpr()->evaluateAsRelocatable(Res, nullptr, nullptr))
+    return false;
 
-  // Some custom fixup types are not valid with symbol 
diff erence expressions
-  if (IsSymbolicDifference) {
-    switch (getKind()) {
-    default:
-      break;
-    case VK_RISCV_LO:
-    case VK_RISCV_HI:
-    case VK_RISCV_PCREL_LO:
-    case VK_RISCV_PCREL_HI:
-    case VK_RISCV_GOT_HI:
-    case VK_RISCV_TPREL_LO:
-    case VK_RISCV_TPREL_HI:
-    case VK_RISCV_TPREL_ADD:
-    case VK_RISCV_TLS_GOT_HI:
-    case VK_RISCV_TLS_GD_HI:
-      return false;
-    }
-  }
-  return getSubExpr()->evaluateAsRelocatable(Res, Layout, Fixup);
+  Res =
+      MCValue::get(Res.getSymA(), Res.getSymB(), Res.getConstant(), getKind());
+  // Custom fixup types are not valid with symbol 
diff erence expressions.
+  return Res.getSymB() ? getKind() == VK_RISCV_None : true;
 }
 
 void RISCVMCExpr::visitUsedExpr(MCStreamer &Streamer) const {

diff  --git a/llvm/test/MC/RISCV/expressions.s b/llvm/test/MC/RISCV/expressions.s
new file mode 100644
index 0000000000000..897004b646368
--- /dev/null
+++ b/llvm/test/MC/RISCV/expressions.s
@@ -0,0 +1,29 @@
+# RUN: not llvm-mc -triple riscv32 -filetype obj %s -o /dev/null 2>&1 | FileCheck %s
+
+.Ltmp1:
+	.quad	tls
+
+	lui a0, %hi(tls+0-.Ltmp1)
+# CHECK: :[[#@LINE-1]]:2: error: expected relocatable expression
+	lw a0, %lo(tls+0-.Ltmp1)(t0)
+# CHECK: :[[#@LINE-1]]:2: error: expected relocatable expression
+	lui a0, %tprel_hi(tls+0-.Ltmp1)
+# CHECK: :[[#@LINE-1]]:2: error: expected relocatable expression
+	add a0, a0, tp, %tprel_add(tls+0-.Ltmp1)
+# CHECK: :[[#@LINE-1]]:2: error: expected relocatable expression
+	addi a0, a0, %tprel_lo(tls+0-.Ltmp1)
+# CHECK: :[[#@LINE-1]]:2: error: expected relocatable expression
+	auipc a0, %tls_ie_pcrel_hi(tls+0-.Ltmp1)
+# CHECK: :[[#@LINE-1]]:2: error: expected relocatable expression
+	auipc a0, %tls_gd_pcrel_hi(tls+0-.Ltmp1)
+# CHECK: :[[#@LINE-1]]:2: error: expected relocatable expression
+	auipc a0, %pcrel_hi(tls-.Ltmp1)
+# CHECK: :[[#@LINE-1]]:2: error: expected relocatable expression
+	auipc a0, %got_pcrel_hi(tls-.Ltmp1)
+# CHECK: :[[#@LINE-1]]:2: error: expected relocatable expression
+	addi a0, a0, %pcrel_lo(tls-.Ltmp1)
+# CHECK: :[[#@LINE-1]]:2: error: expected relocatable expression
+
+#	tail tls+32
+#	tail tls-tls
+# _ :[[#@LINE-1]]:2: error: expected relocatable expression